he doesn’t have much in his life apart from me, doesn’t have many friends, still lives at home etc. I feel so rubbish and part of me wants to just ring him and get back with him, and ignore my feelings and be with him just so he’s happy. I literally can’t bear the thought of him being so sad

He has his family. He has a few friends. And most importantly he has himself. Not a very pleasant thing to say about someone you say you care about. You’re clearly not looking past your own self. Have you done anything to encourage him to move out? Make more friends? These are the things you find out about someone in the first few weeks and you either know it’s not a deal breaker or it is. You accept and help or you don’t and move on.