Look, external motivation from you is very unlikely going to work, especially in the long term. He'll do some job searching and try to socialize, but that's only to try to please you. This guy is not getting any consequences of not trying. He has food, accommodation and a girlfriend. Why would he try to get change?

Whats best for you and what's best for him is pretty aligned. You say, thanks for all the memories, but I refuse to be dragged down with you. Goodbye

If you make it sound like it was your fault and not his, he's going to end up resenting you more and not get up and do something about his own situation