I don't really see that you did anything wrong. It doesn't look like you cheated on your boyfriend.
I was unfaithful with my boyfriend about a year ago. Our conditions of getting back together was each of us were in counseling, we went to couple's therapy, and went to an IMAGO couple's workshop to relearn how to talk to each other.
Though I do think he is being rather abusive by telling you he has thoughts of harming you. To me that's a giant red flag.