can anybody help me with a small problem?

so I am not an extremely social person, quite the opposite,actually.i prefer to keep my head down. the girl of my dreams and me were together, when she decided it wouldnt work and to date someone else, but didnt tell me for a while. we remained friends (and a little more, sorta) for a few months. I had a suspicion that this new boyfriend was a drinker (not jealousy actual suspicion id had it for a while) and he definitely fits the bill for abusive, and telling that to her created distrust. now she doesnt talk to me she hates me and ik its my fault and probably what i deserve. i ended up telling her boyfriend because i felt he deserved to know whats been up. except now im in trouble. was i within my rights or am i not. im sorry this is so long and thank you for reading it