Psychology Today 7 years itch
Steve and Megan met and fell in love while in college. They both shared the same sense of humor, both were politically liberal, but Steve was outgoing while Megan was shy. Steve saw Megan's quietness as intriguing and comforting, Megan admired Steve's ability to reach out to strangers, and even enjoyed his dragging her to parties that she would never go to alone. There was a physical chemistry between them, but also a psychological one shaped by their childhood experiences, past dating relationships, and emotional needs at that point in time.
When they met, each, like every couple, had something at the top of their list of needs. Megan, for example, had recently ended a relationship with a controlling abusive boyfriend, and she constantly worried about her depressed, withdrawn father; what she appreciated the most is Steve's gentle humor and support. Steve was still emotionally reeling from the recent death of his mother; Megan's quietness reminded him of her, and this, in turn, allowed him to open up and grieve. They were probably were not fully of aware of these needs at the time, or fully able to articulate what they felt, but had you asked them what most attracted them to each other, these are the elements they would claim.
And so they got married. They unconsciously made a psychological deal: I will give you this (my outgoingness, my energy and humor) if you give me that (your quiet support). In the first year of marriage, they worked out routines and rules about how they would live together: who would take out the garbage, who would initiate sex, how often they would see Megan's parents, what they do when they got angry - all those things needed to stay sane and create a somewhat settled life.
They also fine-tuned their vision of their relationship and future: Both work to save money to buy a house. Have a child or two. Megan could stay home or work part time. Steve would commute to the city and focus on climbing up the career ladder. Good to go.
Except things begin to change. By year 6, or 7 there is a shift. They find themselves moving into parallel lives with Steve working until 8:00 most nights, Megan spending Saturdays with the kids or visiting her mother. The time they spend time together often seems boring or too routine. And what was most attractive now turns into an annoyance. Steve's outgoingness now seems to Megan a distraction, his humor now seems to slide into a cruel sarcasm, while Megan's quietness now seems to Steve like indecision, a passivity that is driving him crazy.