I don't even think that I can tell you why I still want to be with him, because I honestly don't know why.
I suspect I know why. By your own admission, you've tended to date guys you treat you poorly, and this guy didn't, at least not at first. He validated you, showed you kindness, and did just enough to lure you in before he dropped the bomb about his addiction.
The cognitive dissonance you must be experiencing as a result of this is like having your neck snapped back. It doesn't make sense. And what you want to go back to is the guy that treated you well in the beginning.
But it doesn't work that way. He put his best face on, but because he's an addict, he can't wear that face for long. He's simply not capable of being a mature, accountable partner in a romantic relationship, even though you really want him to be.
Get rid of him, and put you first.