<human>: I'm in a bit of a dilemma here. One of my best friends (let's call him A) has recently started becoming very close to my other friends (B) girlfriend (C).

Just for some addition info, A and B are also both friends.

They've only been talking for a few weeks now and it's gone from regular chatting to dirty talk etc. The girl is now hiding these chats from her boyfriend.

I've already told him how I feel about it and he's just got a general idgaf attitude. I feel kind of sick because I don't really want to get involved because there's a risk of losing both friends but it doesn't feel right sitting doing nothing when one of my friends could end up getting hurt.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: Friend is close to cheating on other friend with his girlfriend. I'm unsure whether I should get involved or leave it.