When my A was very terribly involved with drinking/using, we would have many bad times, and occassionally there would be a magically nice time.
I would become glamoured by that, because the good stuff was so elusive, I would feel its intensity more deeply.
It can be a trick of the mind. Just try to keep yourself clear of glamourizing what is/was really happenening between you.
You can love him, but at what cost?
Maybe you can love him from over here, while he is over there, doing whatever it is that he does.