I'm sorry for your pain but I can't help but say "Halllalujah!!!!"...
Your mom offering you the oppty to move 400 miles from this relationship is God's Grace in action....and you can now walk away guilt free.
He broke up with you...he gave you an out and an excellent oppty came your way. You needed to be free of him and whether you realize it or not...you will be better for it!
So pack your bags, do not...Do NOT...tell him, have a conversation with him, discuss your 'relationship' etc.... use whatever excuse you need to in order to avoid talking to him. You don't owe him a thing.
but I know you seem like a person that would feel bad if you hid all this from him then up and left even though it is because of his own actions that started it...so write a letter.
You can just keep it.....you'll feel better just writing it all down...or mail it...I mean he's going to be 400 miles away... whatever you feel safe doing.
and move on.
You deserve a man that is not an addict.
Keep telling yourself that .....because it is true.