Wait - in another thread you said there was no such thing as dating for Roma:
Sounds like the kid is doing some serious dating. So isn’t he already outside of your culture? Was he raised in America? If so he probably doesn’t see this stuff remotely the same way. If he is dating people of other backgrounds it sounds like he doesn’t value the culture in the extreme way you do - he might not even particularly identify with it. In that case you are the only one who is making the mountain out of a molehill in dragging race/religion into this. You’re only making things worse.
On way to make it better. Just encourage him to marry the girl.
Then he’s no longer Roma, and presumably no longer your problem, since you don’t deal with people outside your own culture. Wash your hands of the whole deal! Bonus - kid gets to escape your house. It’s win-win!