I'm not sure but it seems the reason you're relationship ended was because you had no self confidence and you were depressed. If that’s the case you have no reason to put any blame on her its your own fault. You said you care about her and want her to be happy but you try to cut off contact with her which obviously doesn't make her happy. You shouldn't be depressed when thinking about your relationship and how it ended that’s just selfish and jealous. You are not the same person you were back then you don't need to feel regret anymore. I would say get over yourself and be there for her because she needs you now but I don't know if you can, considering your mental state. I know the feeling and it took me three years to get over similar feelings so my advice is fairly hypocritical however I was able to become close friends with a girl I dated for 8 months. It's all a matter of where you put your mind. If you want her to be happy your choice is obvious.