IIRC the MC is blindsided by his wife at a party when she declares her intention of leaving with another man, a mutual friend of theirs, and continuing a relationship with both men on a sort of time-share basis. I think the MC rejects the idea and leaves, but I am not sure. TIA for any suggestions.
It might be StangStar06's story Too Late to Say Goodbye, although some of the story details don't really match.
Thanks for the reply. Its not the story I was looking for. The main character and his wife are at a neighborhood party. I am not sure if he catches her with someone else or if she just tells him that she is intending to spend the night with a friend - I think the friend may have recently lost his wife. She tells her husband she has always been in love with this friend and that she loves both men equally and wants to share her time between them.
He is not impressed with this and I think he either just leaves her or divorces her and ends up living in another state completely. Although she is relatively happy living with the neighbor she realises that she has just exchanged one satisfying relationship for another and has not become happier or more satisfied - which she had been hoping for.