I'm 37 and I've been seeing a 47 year old man for over 3 years and have lived with him for almost 2 of them. We met around the time that I realized, after almost 20 years of dating, that I did not feel the desire to have a monogamous relationship or have children. We have an open relationship where we both see other people casually, but we are each other's primary. It has taken a lot of work and communication to make sure that both of us (especially me since this is my first non-monogamous relationship) are comfortable and what our boundaries are, etc. 

The issue is a woman he met around the same time as me. He fell for this woman in a different way and proclaims it's the only time he ever considered giving up this lifestyle for someone. She moved across the country while we were still casually dating and it devastated him. She told him he wasn't good enough or rich enough to impress her family anyways. He always prioritized her back then, but it didn't bother me because I was still dating other people looking for a primary.

Well, she came back over the holidays and he met up with her twice. I figured it out by catching him in a lie and confronted him. He said he only lied about who he was with because he knew it would hurt me. He also said that it ended badly anyways and that he limited their time to two visits even though she invited him to spend the whole 10 days with her. He has made it clear in the past that he would dump me or anyone else in a heartbeat for her, but he also doesn't believe that would ever happen. I'm crushed. He truly does treat me like gold other than in this particular area. Am I fool to stay with him and hope that she doesn't keep coming back into his/our life? This is the second time in 2 years that I know of that she has reached out when she is local.