It's suprisingly common in gay relationships, where I used to work one of the questions we'd ask was about domestic abuse and a lot of the gays, especially black ones, would tick yes. I personally know of 3 of my friends that have been in some kind of abusive relatioship, my current boyfriend had to drag me out of my last mess because he could see where it was going

I mean if women can mentally and physically abuse a man in a relationship, what's stopping it happening to two men.
Most times it's not about the who's bigger and stronger, but the actual dynamics of a relationship itself, there is always going to be a more dominant force in a relationship whether it's concious or not and emotions skewers a lot of perspectives whilst your IN that relationship, you may tolerate things in that relationsip you nesscarlu wouldn't if you weren't in that situation. A lot of gay couples feel they have to stick it out because A. Finding a relationship is hard enough in the gay community, B. They feel like they won't find anyone better. and C. They think it's not abuse because it's 2 men.
Add to the fact you have the whole top and bottom dynmanic, the pressure of black men in relationships still keeping it a secret from the general public, DL culture, internalized homophobia, jealousy, fsmily expectations, pride and all the other bits and pieces that exist in other toxic relationships.
And a lot of ethnic gay men are still trawling through their own trauma and issue's...now imagine adding the pressure of a realtionship to that

It's no excuse but it'd def under-reported.