<human>: I am in an open marriage and so is my boyfriend. We, obviously, are not married to each other. 

Until recently, I thought his marriage was just like mine-- solid, open communication, good on the rules of what can and cannot happen with other partners. 

A few weeks ago he called me, very upset, because his wife had suddenly announced that she wanted a divorce. She won't go to counseling. Won't work on fixing it. Makes up really dumb excuses
for why they can't work it out. 

I've been around the block and I really think that she's fallen in love with one of her secondary partners and instead of pulling back and reconnecting with him, maybe even closing their marriage for a while, she's let that get out of control to the point where she's lost interest in the marriage. 

My question is, should I tell him this and if so, how? "Have you considered that all of this is coming from one of her other relationships?" or do I just throw out this theory? 

I think that having this info, if it's true, will help him navigate this divorce and help him understand his feelings and feel less crazy. 

Also- should I cut it off with him? I care about him a lot but I cannot put my marriage in jeopardy and therefore can't act as a stand-in wife at this time.

Can you summarize the given text in a few sentences?
<bot>: did you know in open marriages it's still possible to cheat? I think my boyfriend's wife might be cheating. Do I tell him?