My ex fiance it ben 3 month since we broke he is engaged now and he sent me a msg comented on my photo should i reply back noway we'll get back i know i want to reply back what should i do?

Ignore him. He's engaged to someone else. If you don't reply, she can't blame you for trying to steal him back. Follow your intuition. If you have doubts that replying is the right thing to do, it probably isn't the right thing to do.