This just happened late last night, and I’m not really sure what to do. For some context, this is one of my close childhood friends who’s partner is also the childhood best friend of my girlfriend (we met each other through them). This makes everything a bit more complicated, in fact the only reason I know is because his girlfriend told mine. The 4 of us are the only people that know about it, and my girlfriend and I currently live on the other side of the country from them. They have been together for over 2 years now and live together.
But anyway, the short version of it is that this is her first relationship, and she’s expressed some interest in experiencing what it’s like to flirt with other guys. As a result, my friend has, in a few select instances, allowed her to try it out when he was close by and knew it wasn’t going to go anywhere. But apparently, she recently met a guy online who she flirted with and ultimately had video sex with this past weekend (she showed herself nude for him to jack off to). She just told my friend about it last night, as well as my girlfriend who’s shocked.
For a little final context, I will say that his girlfriend has lived a shitty, sheltered life and can be a bit naive as a result. Her grandmother also just passed away and she’s in the middle of helping to plan the funeral. She also feels terrible about what she did from her conversations with my girlfriend. But that doesn’t excuse what happened, which is absolutely cheating imo. So I told my friend that I know about the situation, and we’re going to talk on the phone today once we’re off work (like I said, I don’t live close by anymore). But I don’t really know what to tell him/how to be there for him. I don’t think he’s quite ready to tell any of our other friends, so I’ll be his main sounding board for now. Honestly I never thought his gf would do anything like this, and my girlfriend can’t believe it either (they’ve been best friends for over a decade). I do believe that she loves him and regrets what she did, but also now I don’t know how to trust that she’ll never do it again.
So I guess my question is, how do I support my friend and do I give any sort of advice about this situation or just kind of let him decide whatever he feels is best?
tl;dr: Friend’s girlfriend cheated on him, how do I support him/what do I tell him?