Just venting here, but welcoming any advice on how to proceed (eg cut him off which will be really emotionally difficult, or give them some space which may take months and possibility our friendship may not recover):
I (34F) have become close friends with my running buddy (37M) while we were training for our respective ultramarathons over the last 2 months. We have known each other for about 1.5 years before this but had only superficial conversations in group settings. This changed when he asked me if I wanted to do a training run with him (I agreed as I was in need of training buddies as I am unfamiliar with the trails and he is confident with them).
During our training time we have had lots of deep and meaningful chats, from mundane issues to relationship advice (my friend seemed to struggle with communication within his marriage and I would provide advice where I could from a female perspective). I would now consider him one of my best friends and he says i am his best friend and we connect outside the running world. I am an extrovert with a really active social life, make friends easily and have many close friends. He is an introvert with a small circle of friends and he says he doesn’t connect with these (male) friends well and is unable to have serious discussions with them.
We are both in long term relationships (both married, he has kids). In the last week, I have separated from my husband (35M) (this was unexpected and sudden) and this friend took me out for hot chocolate so that I could debrief and so he could support me in person. We were out for around an hour.
When he got home, his wife (36F) was upset. She couldn’t understand how we could be such close friends in a short amount of time that I would turn to him in this situation (not realising I also have many other people I have turned to). She accused him of cheating and demanded to read all our messages. She was upset he had discussed their marital issues with me and accepted that he was not cheating, but is still uncomfortable with our friendship. He contacted me to apologise and say that he has to take a step back from our relationship but we can still hang out in group settings.
He has since messaged me and said he feels so guilty for abandoning me in my time of need and still wants to talk and be there for his best friend. I feel uneasy as I don’t want to cause trouble in their relationship (particularly given my sadness about my own marriage breakdown). My husband and I are amicable and I have discussed this with him to ensure he did not feel the same way. He said we did make fast friends but this is not out of character for me, but questioned whether it is out of character for my friend. Furthermore my friend had met my husband a couple of times (although very briefly). I feel regret that I never had the opportunity to meet my friend’s wife previously so that she would know that I simply have a big social life and am not a threat. I don’t want to lose my friend but it is a difficult situation.
TL;DR my best friend’s wife thought he was cheating with me, but I just have a big social life and they may have had cracks in their marriage.