I don't know if this is helpful or not but, I'll share this.
In a totally dysfunctional relationship I was in, we broke up, but kept in contact. Long story short, decided to give it another try after about 6-8 weeks - this was my idea, I just wasn't done yet.
So we did. The good news is this "cured" me of any desire to be around this person.
I got the chance to revisit the relationship and it was a disaster. Not in the blow up fights kind of way.
The thing is I KNEW from the beginning there were red flags all over the place, but they were kind of small-ish to start and I chose to ignore them.
By the time we got to round 2, he had removed any mask of any kind of normal-ness lol. I am grateful I got to see round 2, it was no fun at all but it put to rest any idea at all that it would ever work and really, finally, a few months after that (stayed in contact again for a bit) put the idea to rest the I ever even wanted to talk to him or see him again. If he called today I would hang up, if he showed up at the door I would close it in his face. Not in anger, in indifference.
Now, why do I tell this story. Well for two reasons. I have a hunch if you spoke to the ex today, you would find a different person. He is not loaded (assuming he is still on the wagon), he isn't hiding behind any particular drug at the moment. The fact that he could really only engage with you on an intimate level when he was drunk/stoned is a pretty good reason to believe he is not who he presented himself to be.
He used drugs to behave and be someone he is not (in my case he had a personality disorder he hid, quite well, until he got tired of hiding).
So what you are missing is no longer there. He may be on the road to recovery now, but he wasn't when you were with him. Sober perhaps (that you know of, you don't really know do you?) but not in recovery.
Anyway, that's the story I wanted to tell, for what it's worth. What you are missing probably doesn't actually exist. The way he has treated you is less than stellar (understatement). Perhaps a little less sympathy for him and a little more anger at that poor treatment is on its way. I hope so for your sake.