Search Results: how to know if he's cheating

Hi! I want to start off with a little background, my friend ( let’s call him K ) and i have known each other since we were kids (10+ years) and are very close. I met his wife ( let’s call her F ) on their wedding day and since have become pretty good friends with her as well i’d say. Him and his wife have been married for just about 1y and a half, and have been together for almost 2y. Now this might be a little hard to keep up with so bare with me please, my issue is that my mother is good friends with F’s ex coworker and saw they were hiring but when I told my mother I was reluctant to work there because of things F had told me, F’s ex coworker told my mother that F left there due to drama she had caused because her coworkers knew she was married yet she had been sleeping with one of the cooks, along with other personal things. I was completely shocked to hear this because i didn’t think F would do something like this. On the other hand, F and I have never hung out without K present, sure we text every so often but I really don’t know much about her besides what I’ve seen when she’s with K. So i’ve been sitting here, extremely conflicted, because i don’t know whether to tell K or not. I don’t have really any solid evidence so even if I do say anything would he believe me? I would really appreciate any kind of advice.