My friend (who I’ll call M) is a transgender man (20) currently obsessed with a guy (I’ll call B) almost double his age. (35)

at first I just brushed it off, just thought it was gonna be a fling, but it’s been probably 5 months now, they aren’t even officially dating just sleeping together. Here’s the thing, I have heard from M and other friends that B VERY frequently misgenders M and doesn’t take his transition seriously. He also acts very weird about the age gap, and from my understanding doesn’t want a relationship (due to that?) but will happily sleep with M.

M has been trans for as long as I’ve known him (5 years) and longer, he presents masc, uses he/him pronouns and is just all around clearly a dude…
I know friends have asked M about how B treats him, and he is constantly brushing it off, saying “oh I don’t want to talk about it”, or “it’s fine” but it clearly isn’t, and clearly upsets him.

This whole situation is upsetting me becuase this is M’s first relationship, and the fact he isn’t being respected in the most basic way hurts to watch.

M is very stubborn too, won’t listen to advice without getting frustrated, there have been times I’ve tried to hint at B not being good for him and it resulted in me being yelled at.

This aggression towards me combined with the frustration of watching this burning building of a “relationship” has made me grow destain towards M, every time I see him, all he talks about is B. I want to support him as a friend, we once had a really close friendship, but it’s becoming harder and harder to be around him while he is with B.

Do you think there is anything I can do in this situation, or do I just sit back and watch the fire burn.