I’m an asexual senior in college. My beloved friend is gay - a freshman. His father was abusive. He only dates abusive guys. How do I show I support his homosexuality... just not his abuse?

You should probably sit down and have a talk with him about your concern about the trend his previous partners all seem to have. Make it absolutely clear that it is this trend and not that he is gay that is the issue. Let him know that you completely accept and appreciate that he is queer and that you are just concerned about him. Maybe even talk about him going to a therapist, abuse might be the only love he really knows and a therapist could help him unlearn this. Please just let him know that it is the personality traits of these people, and not their gender.