I'm amazed by your strength. Especially to put yourself through medical school despite the turbulence around you. Perhaps your last bullet point says it all; it sounds like you know you'd be better off moving on from M. He has been supportive in ways, but he has hurt you in ways. He taught you to cry silently. He told you you need to fix yourself when you've been the one actually taking steps toward your future--and his. I know I don't know the whole picture and that he has wonderful qualities, too. But sometimes, even if a person has been a true gift in our life, we have to acknowledge that souls and lives can evolve in different directions over time, and that's okay.

I feel like I'm so under-qualified to give any advice here, but I didn't want to get to the end of your story and not say anything. It's amazing how many kind people there are in the world. It seems so scary to leave a security blanket-- but you will make new friends, and you will very likely meet a man who is supportive, loving, and caring and can contribute positively to your healing process. I don't mean that as a flippant remark, though I recognize it's much easier to just say than to actually go out and manifest in reality. But I honestly mean there are billions of people in the world, and people will often find each other. There are many good, kind, safe men and women in this world.

After med school is a great time for change. Residency is a great place to start fresh, make new friends, be distracted by long hours, immerse yourself in a new community, learn new things. I'd try for residencies in cities. Boston, New York, San Francisco, Atlanta, Seattle (I realize I've made the assumption you're in the US).
I was also struck at the end that your life goal is to play music? Even if it felt scary to take the full plunge and try out a full-on music career now, there are a lot of ways to play music recreationally to ease into it. I've been part of several local, open music ensembles that build excellent support systems for people, giving people a home when they thought they were alone in the city. In a city, you can busk, too. You sound like you have a strong resilient streak in you, and that is an admirable thing. Sending hugs...