We have only to look at the divorce rate—41% for first marriages, 60% for second marriages, and a whopping 73% for third marriages (http://www.divorcerate.org/)—to know that people often fall out of love with their spouse. Why do so many people fall out of love?
Don, 37 and Megan, 32, fell passionately 'in love' soon after meeting. They had fiery chemistry and loved being together. Now, two years into their marriage, the passion is gone and they both believe they made a mistake. But did they?
Don was brought up to believe that his good feelings had to come from a woman's love. Both his parents role-modeled self-abandonment for their own feelings of worth and lovability and made each other responsible for their happiness. Don's mother took way too much responsibility for Don's feelings, so he grew up believing that his partner was responsible for his feelings.
Megan grew up with two very needy parents, who both made her responsible for their feelings. She became a caretaker, taking responsibility for their feelings and wellbeing, and learning to ignore her own.
Since we come together at our common level of woundedness—our common level of self-abandonment—Don and Megan were perfect for each other. They fell passionately 'in love' because Megan's wounded self did a great job of caretaking Don's feelings. Don felt loved by Megan, and Megan felt needed by Don.
The problem was that Megan couldn't possibly meet all of Don's needs, and when she didn't, he was angry and miserable. The more miserable he become, the more guilty and responsible Megan felt. Anger, misery and guilt do not create passion.