I know exactly how you feel. I entered a relationship at a young age too, and it lasted a good few years, and afterwards when he moved on it was clear as day that he was not giving me everything I needed, and that he never could have, and it was the one incompatibility - amongst all the perfect compatibilities that held us together so long - that is impossible to change because it is just...well...HIM.
My biggest mistake? I DID contact him. And now and again he contacted me. We even slept together for a while too, and it is all a massive regret. We were trying to draw upon something that we no longer have, that is cold history now, and the going back to him and keeping contact with him... it has now made me a mess. I feel with all my heart that I want him, when he is not right for me.
PLEASE save yourself the pain. He has had hard times, yes, but don't cave for the pity vote. It has ended. I know exactly how it feels to have those strong, uncontrollable passions for eachother that hang around. I know you feel that despite it all, you two are inevitably drawn to eachother and that 'means something'. But really, it doesn't. Its just the memories and nostalgia of something that probably lasted longer than it should have in the first place.
It is a weird thing, how much you can want them, and they want you, after a breakup. But it is a damaging thing, and something to avoid out of respect for yourself. And guys handle this differently, and are often far more emotionally adept at moving on, and generally move on it a much more productive fashion - ie. going out there and seeing who else is around.
Try to do the same. You will be fine. You sound a million times more capable and strong than I did after my breakup. It seems, deep down, you truly know that it is over and finished with.
All the best!