He doesn’t need citizenship to live in the US as long as he has green card. It’s a very personal decision and not something one needs to be pushed to do. I’d not get citizenship because someone thinks I should. Green card gives him all the same rights ( minus voting).

Saying that, him spreading STD and sleeping around without protection is a different story. I am not sure he wanted love and compassion. He likely wouldn’t be going around contracting and spreading STDs. Him leaving you is a blessing. Please cut all ties so you can heal and move on.