My boyfriend is going into rehab. Should I trust it will work, or just give up?

My boyfriend is addicted to the prescription drug Oxycontin. He used to be the sweetest, most caring person I’d ever met. He made me so happy, and was considerate of everyone around him. Then he started to change, and I found out that he was using Oxycontin “once in a while”. This was not the case at all; it became very apparent that he has a full blown addiction. He has been a vicious monster, a wreck of a human being. All he has been talking about is wanting to die, he picks fights with me and says horrible things, steals and lies. He got out of a five day detox center about a week and a half ago, which I was overjoyed he decided to try. It did no good, and he relapsed within a day of getting out. Today he moved into a 30-day sober living facility. Before he left he wasn’t as loving as he usually was, he was jaded and depressed. We didn’t even have a proper goodbye, he wasn’t emotionally present at all. Now, I need advice on where to go from here. Part of me is screaming “Run! He will never change, and when he gets out he will still be an addict and you will find out quickly that your optimism is for naught.” However, the other part is saying “If you assume it won’t work and leave when he’s gone, and he gets out ready to start clean and sober, you will shock him back into using and miss out on a great life with him.” Has anyone else been in this situation? Has rehab actually made anyone permanently sober after 30 days of treatment? Please help, I’ve hit rock bottom.