Romeo and Juliet (including Romeo's infatuation with Rosaline) are the characters that display young love, and their parents show the traditional "love" relationships in marriage during Shakespeare's day.
Romeo spends Act I, scene i moping about the stage. He talks about how long the day seems when one is "sad," and describes how desperate his love for Rosaline is:
Love is a smoke made with the fume of sighs,
Being purg'd, a fire sparkling in lovers' eyes,
Being vex'd, a sea nourish'd with lovers' tears.
What is it else? A madness most discreet...
He is describing the desperation he feels, being in love with someone who will not return his feelings, and, even today, we think of this as infatuation rather than love and associate it with young people falling in love for the first time. His feelings for Juliet begin the same way, only transforming to something more mature as the events of the play test the depth of their love.
The best example of more mature, married love in the play is the relationship between Lord and Lady Capulet. This is a very traditional relationship in which Lord Capulet is the master and ruler of his home and there are no visible signs of affection between them. In Shakespeare's day, it would have been very common for men and young women in the Capulet's social sphere to marry by way of contract between father and future husband, the securing of a girl's hand in marriage being a sort of business deal. Lord and Lady Capulet conform to this traditional model.
In Act III, scene v, Capulet really loses his cool when Juliet refuses to marry Paris, a match that he, the father, has set up. He really goes off on her and there is a suggestion that there might be some sort of violence. Lady Capulet attempts to intercede, but Capulet is the firm ruler of this household and ignores her. Once he has left and Juliet pleads to her mother for help, Lady Capulet's only response is:
Talk not to me, for I'll not speak a word.
Do as thou wilt, for I have done with thee.
And, abandoned by both her parents, Juliet makes the fateful trip to the Friar's for the sleeping potion that will lead to her own and Romeo's deaths.
Lord and Lady Capulet show the audience the traditional marriage roles, an apparent lack of passion in a household firmly ruled by the husband. Romeo and Juliet go against all the authority in the play to fulfill their secret passionate love for each other. They even defy the long-standing feud that exists between their families in order to follow their hearts.