Hey Kay! Sorry that you are going through the motions of anger right now. I totally get that you are frustrated with the energy that you put forth into this relationship. You feel unappreciated and that you wasted time. I feel the same about my relationship.
The thing about your guy is that no one else is going to take him. You become that which you associate with. So, any young and respectable lady isn't going to be abusing drugs. Of course he is living with them. He is an addict and can't provide for himself, so he wil and he is going to take what he can get, living with them for as long as they provide for him. He doesn't care that she is 14 - she is some one to support him who he may be able to use with and she has a mother who is willing to take him in. He isn't looking for a deep emotional connection - if he is actively using, he is looking for dope.
I would not be angry - I would take this a lesson. Birds of a feather flock together. He chooses to associate with these people, but you do NOT choose to associate with these people, therefore, the common ground for socializing with him isn't there anymore. Block him and the chick on facebook, change your number, and thank GOD that you AREN'T THAT girl. He WILL use her and that is ALL he will do.
Best of luck and much love your way!
YG