As for your question about people bailing on relationships after rehab, yes, I've heard that a few times. Could be that they want to start fresh, could be that they want to leave all that hurt and pain they caused behind, could be that they aren't thinking straight, well that's kind of a given, the not thinking straight.
^ so when you say this, does this mean he very well could be sober even with the red flags and just lost feelings for me but never communicated them and stuck it out if he is in recovery?? Is this likely possibility 
? It's impossible to say. What I was actually saying though is this is a not uncommon thing that happens. Recovery is not instant, it certainly doesn't take a month. His brain didn't all of a sudden sort itself out after years of drug use.
It takes months or years for a person to feel "normal" again. He was in rehab in August, out for a month then broke up with you to go hang out with his "former" dealer. If this dealer is on such a good path, why would he be deleting his texts, why would he lie about not knowing why he's texting?
No need for him to lie unless he's hiding something to do with the dealer right?
I also take from your question about marijuana that he was smoking that? People that are sober and in recovery aren't using drugs, that's the whole point.
Addicts are very selfish, as I'm sure you experienced. Maybe he just decided he wanted to party all the time. It's kind of impossible to say.
But again, I doubt he knows what he's doing.
It's not you by the way, as Aries mentioned - it's about addiction.