When did he go in? He might just need space right now, might feel ashamed, guilty, depressed, is busy getting to know others, is working hard in therapy.. really could be anything. I hate to say this, but I have to agree with Caseface, he might be feeling radically different right now.
But honestly space is important sometimes when first getting sober.
Also, I know it has to fucking suck to put up with him throughout all his bullshit and then have him not call you. They often say recovery is a selfish act and they are not lying. I personally am really ashamed that my drug use interfered with me ever really forming a romantic relationship with another but it does have its benefits. I have no kids or significant other. Makes it easier to focus on me! Also, as far as relationships go, I think I am going to have to get with someone who really understand what a struggle addiction is. If that ever happens. Its not really up to me at this point. I do know right now I am not fucking ready for a relationship beyond love for my family and friends.
Also, honestly consider if its worth it. Because this shit is not fixed overnight (its not ever really "fixed" per say, just can be managed correctly). I am an addict/alcoholic for life, I am okay with that today. What doesn't kill you makes you stronger and it gives me additional empathy (and believe me Social Work requires a fuckload of that).