please, please, please don't feel guilty, sobernow. It is not your fault. Look at all the people in their twenties who end relationships - waht person hasn't got a story of heartbreak behind them? yet they go on to build another life. My very best and oldest friend - literally the boy down the road, the first boy I fancied, the boy I went to school with, the nearest thing I have to a brother died an alcoholic when he was 46 last year. A similar story to yours, though I never actually went out with him. He always phoned me, wanted me in his life. We were linked and people saw the link. But he was so mixed up, very paranoid, in and out of mental hospitals, on lots of medication for nearly 30 years. All that was nothing to do with any one person. He never really blamed me but at the back of my mind I kept thinking, could I have saved him? Then I imagined what my life would be like if I had lived with him. I know I couldn't have stopped him. Think of all the people who do live with alcoholics - it takes more than their love and devotion to sort out their problems. It has to come from them.
I am really sorry people have said to you 'he never got over you deserting him' That is so cruel and unthinking. Your boyfriend may well have had a problem at the time with rejection - any rejection - but no one saw it until it happened. My friend blamed the start of his problems on the death of his grandmother - a death that was bound to happen one day. If it hadn't been that I think it would have been something similar. The crisis was waiting to happen. It just took an event to set it in motion.
Please be kind to yourself.
hugsXX