Before John's schizophrenia is diagnosed, he and Alicia enjoy a fairly normal, stable marriage. They have a child, and John secures a high-paying job at a prestigious laboratory that does work for the Department of Defense. Because of the classified nature of John's work, Alicia does not know that he is slowly losing his grip on reality. Even after a doctor informs her John is mentally ill, she does not initially believe him.

After she knows the truth, Alicia demonstrates her love to him primarily by continuing to support him, caring for their child and making sure he takes his medicine, etc., but it is hard on her. John's medication saps his energy and dampens their sex life, which eventually drives John to stop taking the medication and leads to further hallucinations. During one of these episodes, he seems about to psychically harm Alicia, causing her to grab her child and get in the car to drive away. This is a pivotal scene in the movie, the point John realizes that the people haunting his imagination are not real. From here on in he gets better, and he and Alicia learn to live as stable a life as possible given John's condition. By the end of the film, it seems they have learned to accept John's illness and not let it spoil their love for each other.

Alicia's first impressions of John, before his diagnosis, are generally positive; she views some of his eccentric behaviors as charming and unique, and she doesn't seem to mind that he seems to live by his own set of rules. She marries John because she loves him, and she probably had rather high expectations for their life together as John's talents were already obvious to her and to his academic community.

When John starts to unravel, Alicia may have experienced a number of difficult emotions. She may have experienced fear, as John's erratic behaviors were beginning to seem unpredictable and almost dangerous, and she may have also experienced self-doubt. Alicia may have questioned her own sanity: how could she have missed such clear signs of shaky mental health in the man she loves? Their relationship is changing as Alicia learns the truth about her husband, and she grows a little distant from John as she tries to figure out what is going on.

After John's diagnosis, Alicia is no longer a young wife with a bright married future ahead and she accepts with some trepidation her new role as primary caregiver of her husband. They have a baby at this point, and she must also worry about looking after their young son and to keep him safe from his father who does not mean to be neglectful of the baby when the voices in his head distract him. Alicia is likely very disappointed that her marriage and her life have taken this turn, but she stands by John and she copes with her own disillusionment and moments of depression.

So even though their relationship is tested by John's illness, Alicia's commitment to him and to their marriage helps him to regain his health and autonomy. By the end of the film, their marriage appears steady and strong, and John honors Alicia by giving her all the credit for his success, which is as loving and heartfelt a message as he could give her.

John Nash's condition greatly impacts his wife on many levels.  The most evident is that it becomes a challenge to maintain a high level of care for someone who is in such dire need of care.  Alicia becomes the primary caretaker for John and their child, knowing that he is unable to help with simple tasks at home such as taking care of their child as well as earning a substantial income.  John's condition begins to drain on their marriage from an intimate standpoint, as well.  The feelings of love and devotion become supplanted with duty and responsibility.  This transforms their marriage.  On a more symbolic level, I think there is some level of challenge endured with John's condition and the determination of "what is or is not real."  John has an increasingly difficult challenge in distilling reality and this transmits to whether the love both Alicia and John share is real.  Since love itself can present itself to be illusory, then it stands to reason that a condition which masks reality could also serve to be a drain on any relationship and probably causes some level of festering in theirs.  Once John learns to "control" his episodes, we don't really get an indepth examination of their relationship.  We see improvement, but we don't really gain insight into why there is such change.  It is almost presumed that once Nash demonstrates control, his relationship with Alicia resumes its original infatuation.  He does credit Alicia with being critical in understanding his own "beautiful mind" through her "beautiful heart."  Yet, I don't think this adequately articulates the challenge of mental illness, especially one as painful as schizophrenia.