Why would a woman agree to be a married man's side girl?

[purplepaisley]

The woman is in love with the man, or maybe not love, but misinterpreted feelings. He feeds her the loving words and the feelings are there when they are together, but he has no intentions to leave his wife and take on a new wife with the same relationship challenges. He doesn't want to deal with divorce and custody and the division of property and all other things involved in divorce. He enjoys his mistress and says all the right things and everyone feels the feels, and the mistress loves him and is anxiously awaiting for him to leave his wife so that they can be an official couple, and that never happens, but she stays in the relationship on pins and needles, waiting. She gets rejected repeatedly on holidays and family gatherings, but next year...next year will be different because he'll leave his wife by then...and that doesn't happen. It's her feelings for him that keeps her in this place.