As I have talked by phone, by email, and in person, with married men and women who have been in lengthy lost love affairs, I have noticed something that surprised me at first: the lost love takes the place of, and emotionally becomes, "the true spouse."
Even when people willingly let go of their lost love affair partners to return to the commitment of their marriages, even when they have chosen their spouses as being better for them than their lost loves, the women in particular have a lot of trouble reconnecting with their husbands sexually—even those who reported having good sexual relationships with their husbands before the reunions. That doesn't necessarily surprise me. What surprised me was the reason that the women (not the men) gave for this: if they have sex with their husbands, they would feel like they were cheating on their lost loves.
Over the course of the sexual affair—with all the reminiscing about past experiences and emotions, then the current emotions and reports of daily living, along with the sexual intensity—the spouses and lost loves change places; the lost love comes to be seen as the real husband, with the actual husband seeming like the interloper.