You seem desperate. It's as if you have received and invitation to a double-suicide and you are weighing your alternatives. I think you too need to talk to a counselor.
You are blaming yourself too much and not recognizing that he is trying to isolate you, to blame his own poor choices on you, and to make you feel guilty for wanting to do well in medicine - the very thing that he wishes he had done himself. Sooner or later we all experience failures in our lives. Your bf has to face the fact that he may or may not realize his dream. It is not your fault! Maybe you feel that you were not as supportive as you ought to have been, but to me it does not sound like he has been that supportive of you either. You sound like a very sensitive and compassionate individual that has painted herself into a corner, an impossible situation, so I really feel for you.
As someone else said, some people need to hit rock bottom before they will start to recover. Life is hard, studying medicine makes it even harder, but you don't need to make it harder still by participating in a mutually destructive relationship. It has not been good for either of you.
I am old. I only happened to read your post because I was reading up on something else that matters to me as a parent and the title caught my eye --"I ruined everything for him". At first I misread it and thought it meant that you threw away your future for a chance of happiness with some boyfriend. Fortunately, you have not done that yet, but I decided to write because you appear to be on the verge. As a grown-up who has had similar experiences and has seen numerous cases of malfunctioning relationships of every shape and complexity, I want to assure you that loving someone to death does not need to lead to death! And, as strange as it may sound to you now, it is a temporary affliction. Maybe you think I am senile, but even if that were to be the case, even after I forget what year it is or the names of my children, I would still remember too well what it feels like to be young and conflicted and seeing the future in very abstract terms, all revolving around romantic visions of happily ever after - or unhappily ever after. It's not really like that. People grow and change. What matters to them change. They get over their failures and sometimes build something better. You will change too. Trust him when he says to stay away, you are probably doing him more harm than good. He needs to get over this himself and meanwhile you need to look after yourself and concentrate on your own studies. Also, bear in mind that there are more weird and wonderful people coming your way that will intrigue you and challenge you and drive you crazy. It will all be hard and confusing but there will also be lots of good times. Save some of your energy for them.