Sorry this is so long, please do read this and help me, I'm so confused, if you want to know anything else about this you can message me or ask me here, I just need some wisdom from ya'll.

I'm so confused right now, I don't know what to do.
I had, a really close friend, he was really close to me and we hung out alot. After he graduatied he left home to live with some relatives, we stayed in touch, we talked on the phone alot and he would come down and visit. All was well then he meet this girl, she is not a very nice person and is involved in a plethra of illegal things. He fell head over heels in love with her moved in with her and her druggie friends and after that the phone calls stopped and when he was in town he wouldn't call me and then lie to me that he was never in town, I knew he was lying because his mom told me he was in town. Last time I spoke to him or saw him was at graduation, I was schocked and touched he came to my graduation and thought that maybe things would change. I found out he is doing drugs and drinking every night and has lost two jobs because of this.
I know he cares, he gave me a huge hug before he left and was tearing up because we never hang out anymore, he told me how much he missed me and that I should stay in touch, I responded why don't you answer my calls and maybe we could do something. He said yeah he would and that he would be in touch next time he was in town, what a lie. I saw his mom two days ago and she asked if he had come to see me, I said no why, she said oh well he was in town last weekend. Now here he is messaging me on Facebook telling me he misses me and that he loves me and I'm his bestfriend in the whole wide world. I don't know if I should message him back or not, I don't want to talk to him, it hurts to much, he isn't the same person, yet I do want to talk to him and tell him everything that has been on my mind, tell him I'm worried about him and that he needs help. I don't know what to do, I'm so hurt and confused, I am almost in tears, I hate to see my friend like this, I hate that he keeps doing this. Somebody help me, I just need some advice, I don't want to see him die or ruin his life. I miss my friend and I don't knwo what to do about it.