In the play Cat on a Hot Tin Roof the characters of Brick and Maggie are in a complete turmoil about sex. There are many veiled references about why Brick won't be intimate with Maggie, and this creates a problem because she 1)equates intimacy with sex, and 2)she would like to have a baby to garner favor with her in-laws. There are even veiled references to the relationship Brick has with his buddy, and whether there was a homosexual relationship between the two.

Since we're talking about films at the moment, I'd offer "A Place in the Sun."  This movie version of Dreiser's "An American Tragedy" presents sex through its product ... a pregnancy.  This turns out to be one of the key elements in the play because Alice (Shelley Winters) gets pregnant just as George (Montgomery Clift) starts to make "progress" with Angela (Elizabeth Taylor), and threatens to ruin George's "hopes" if he doesn't marry her.  From there it works out pretty much like the novel ....

It's Dreiser at his purest ... a young man controlled by powers he "can't" control (lust/sex/money), and who is destroyed because of his inability to deal with any/all of them.  It's easy to get, and I think you'd enjoy it, although it is an older movie and not up to today's "effects" standard ... although it's head and shoulders above many of them for plot.

In the movie "Stardust" the protagonist Tristan and the star, Yvaine, stay together at an inn at the end of their long journey. Sex is assumed by the audience as it shows her bathing and him standing on the other side of the screen speaking to her. Then, in the morning, she wakes up on one side of the bed, with the other side empty, looking for Tristan. She appears to be nude under the sheet. This affects characterization in that the relationship between the two is clearly on another level as he goes off on his own to break off a relationship with another girl the next morning. Yvaine, not realizing why he left, wanders off in despair, thinking he has used her and left her and finds herself at the hands of an enemy. Had they not spent that night together perhaps she would have been more alert and the ending would have been very different.

I am not sure if this applies, but the idea of sex being described and not fully articulated or realized could be present in the film American Beauty.  Lester Burnham's fixation with teenager Angela is one where sex is implied, but never actualized.  The idea of sex in this setting is one that represents flight, the ability to dream and allows Lester to "look closer" at his own life, setting in motion the events that allow him to understand his own sense of what should be as opposed to what is, but also brings him closer to his seemingly inevitable destruction.

In The Great Gatsby, Fitzgerald establishes the sexual relationship between Gatsby and Daisy without detailing their encounters. The two became lovers when they first met in Louisville where Gatsby was stationed before going overseas to World War I. Fitzgerald alludes to their relationship in this passage:

. . . [Gatsby] was at present a penniless young man without a past, and at any moment the invisible cloak of his uniform might slip from his shoulders. So he made the most of his time. He took what he could get, ravenously and unscrupulously--eventually he took Daisy one still October night, took her because he had no real right to touch her hand.

Gatsby, much to his surprise, realized that "it didn't turn out as he had imagined." He fell in love with Daisy: "He felt married to her, that was all."

When Daisy and Gatsby reunite in West Egg five years later, Fitzgerald suggests subtly that they resumed their sexual relationship. Gatsby had thrown many huge parties, where people came to his mansion "by the hundreds," hoping that Daisy would wander in. After he and Daisy do meet again, however, the parties stop abruptly, Gatsby fires all his servants, and hires new people through Wolfsheim. Gatsby explained this change to Nick:

I wanted somebody who wouldn't gossip. Daisy comes over quite often--in the afternoons.

The physical relationship between Gatsby and Daisy survived a five-year separation, which led Gatsby to believe that his dream of their being together and wiping out the past would be realized. As Nick observed, "his dream must have seemed so close that he could hardly fail to grasp it." He never would, of course, or ever could, which suggests a major theme in the novel. A romantic dream stands no chance when pitted against the corruption of modern American life.

What novel or movie suggests but does not describe sex? How does it affect the theme?

As litteacher8 suggested, many Victorian novels do not speak out right about sex as it was considered inappropriate for people to read about sex in novels.

Thomas Hardy however deals primarily with a rape in his novel Tess of the d'Urbervilles and while he does not come out and say that Tess was raped. He alludes to this at the end of one of the chapters and then picks up the next section of the novel with the unmarried Tess as a pregnant young girl.

Throughout the novel, Hardy shows how Tess's life is ruined by this one event and how pure and innocent she is although society will not accept a ruined woman. The villain, rapist, consistently blames Tess for the sexual act as if she was asking for it. Hardy however illustrates that this "ruining" was not Tess's fault at all through her characterization and actions. Victorian society would not have allowed a woman to be blamelss in a case of premarital sex. Rape was not a vocabulary word to them.

Another movie that simply suggests sexual relations is Splendor in the Grass with Warren Beatty and Nathalie Woods, who are a young couple in love at the time of the Great Depression.  But, Deanie's mother telling her not to "spoil herself," Bud finds another girl to satisfy him.  Nevertheless, Warren's character, Bud, yet loves Deanie, who goes insane when she understands what has happened.

After spending three years and six months in a mental institution, Deanie returns home to learn that Bub has become a farmer and married an Italian girl from his college days.  Then, they both realize that they must continue their lives.

In Kate Chopin's The Awakening, the main character, Edna Pontieller falls in love with a young man, Robert -- a man other than her husband.  What is interesting is that they never have a sexual relationship although they are very close.  Edna does, however, have a sexual fling with a man that she hardly cares about and certainly isn't emotionally invested in.  The scene is not explicit in the least, but her actions certainly affect us as readers as we see the continuing development of Edna's character.

One of my all-time favorite movies is A Summer Place. It is just full of sex, but the most you ever see onscreen is a chaste kiss. The plot of the story is that a former handyman at a New England inn has become wealthy and has brought his wife and daughter to the inn for the summer. When he worked at the inn, he had fell in love with a girl who also worked there, and who now happens to be married to the inn's owner. They rekindle their romance, are eventually discovered, and end up divorcing their spouses and marrying each other.

Meanwhile, his teenage daughter and her teenage son discover each other and fall madly in love. They manage to keep their virginity all that summer--even though her mother is insanely suspicious of them. One afternoon, the sail out to a nearby island and get caught in a storm. They have to stay on that island all night until the storm lets up. When they finally get back to the inn, her mother is waiting with a doctor who is going to examine her to make sure she is still a virgin. After their parents' divorce and remarriage, the two teenagers are still in love and find ways to be together. It's complicated, but she ends up getting pregnant--and all we ever know is that they can't stop thinking about being bad!!

The Sun Also Rises by Hemingway -

Brett Ashley is a socialite who bounces from man to man, all while Jake is hopelessly in love with her. She has implied sexual relationships with Mike and Romero the bullfighter. Jake also implies that his war injury left him impotent, but Lady Brett is unwilling to give up on sex, even if she truly loves Jake.

In Tennessee William's "A Streetcar Named Desire" the rape of Blanche (sex in its most violent form) is not depicted in the play. It is alluded to. The film follows the same conventions. We see the lead-in, the violence, but not the act of sex/rape itself and this makes the moment and the aftermath all the more powerful. Because we do not see what has occurred, much the same as Stella does not see what Stanley did to her sister, we can choose to avert our eyes from what it has done to the already broken and fragile Blanche.The rape finishes the task of destroying Blanche's tentative grasp of sanity, it breaks the relationship between Stella and her husband through the erosion of trust, it destroys and chance Mitch has of ever letting go of the lies and giving Blanche a chance - and it also makes him confirm his opinions on love, I think. I feel Mitch will now end up as a bachelor forever.

A movie with a famous example of a suggestion of intimacy is West Side Story. Tony and Maria have just sung their brilliant duet, "Tonight." The camera pans across to a wall and the lights fade out. This develops the plot and characterization so that Tony's death has the greatest possible meaning for Maria.

This is very common in Victorian novels. To outwardly describe anything sexual would have been improper. So instead we get descriptions of dinners, dances, walks in the countryside and carriage rides. Sexual tension is present throughout, and there is even hints that the deed has been done. But we never actually see it.

Probably the most famous example of this sort of scene that can be found  in the movies is in Gone With the Wind. There's a scene where Rhett Butler is drunk, and he tells Scarlett O'Hara that he loves her; it's not a pleasant conversation, however. Scarlett breaks off the conversation and walks away from Rhett. Suddenly Rhett runs up behind her and sweeps Scarlett up into his arms, kisses her rather violently, and then carries her up the grand staircase. That's where teh scene ends, but it's impossible to watch it and not know what happens behind that closed bedroom door at the top of the stairs. Take a look at the link below to see this scene for yourself.

This is a major turning point for the plot of Gone With the Wind. Before this Rhett has been playing it cool and Scarlett has been pining for another man. This scene lets us know that they have become lovers. The overt sexiness of the scene was a very big deal when the movie was released in 1939.