Wow your ex sounds like an absolutely horrible person. He never should have said that to you, and clearly it was a blessing that relationship ended. Have you been in therapy (and I don't mean speech therapy)? If it never really bothered you before his words, then a lot of the problem is likely psychological, and you can get back to a good place. There's no real medication unfortunately. Some people have anecdotally found various drugs helpful off label, but then they do the opposite to others.