His behaviors sound very common for people with substance abuse problems. Very sad. But you didn’t cause it and you can’t fix it and you can’t change it but if he wants to seek help, it’s available.

You have to live your own life though. It’s too short to worry why somebody is distant. I get it. You are quite attached but do get busy with other stuff, there is no benefit in making him the center of your world. There is more to life. You can do it.