My gut instincts are killing me.

Hello everyone, I (38m)been a follower for sometime now and finally want to post. It's been 2 years now since this incident. My wife (39f) has been diagnosed with bp1 w/manic depression. A couple she met on Facebook(New ppl that moved from a different state) that was a town over wanted/looking to make new friends. My wife made friends with them. Everything was going fine until the last 6 months of the "friendship" they started to invite us to the bars in town. (I am not a bar person.) In the last 6 months of it, I've happen to see my wife video chatting to the friends husband on messenger while he was only wearing his boxers. Once he saw me he stepped away to put some clothes on. Made inappropriate physical contact on my wife.(Was the last time we went to the bar. I put an end to it.) She stayed the night over there while the husband was out of town for work, she came home thanking me for letting her hang out with her girl friend because she was by herself and wanted my wife's help to pack stuff up because they were moving. BUT here's the kicker this is all that crap that makes me question everything. We had a talk before bed that she told me she feels like we only have sex but like its meaningless. Like I was just using her. We used to have sex 2-3 a week and now only maybe 1 time a month. Then she blames it on her medications. She has been taking medication for over 7 years and now of a sudden during that time period everything halted. She told me nothing has happened. But my freaking mind just won't let it go. Don't get me wrong it'll pop in my head maybe 1-2 times a month or more. Wtf do I do, it's making me build resentment towards her.

Edited a few words.

Tl;Dr my wife may or may not did something, but because all the events makes me believe she's being deceitful.