This urge to "nurse damaged people" can come from something in you that is good and strong, but has been channeled in a perverse direction. You can find a better outlet for your capacity to be understanding of broken people.

What you think of as "love" may actually be something else. I think when loving people do not have a suitable object for their devotion, they channel it into what is not really an object of love. Real love may be unconditional, but that doesn't mean that it can just be aroused by anyone and anything. Real love is based on there being something lovable to love. A child does not truly love a doll or a teddy bear. A child goes through the motions of loving the doll or stuffed animal, but that is not truly love. I guess it's kind of like a "practice" love. You probably had dolls or soft cuddly animals that you felt "love" for. Do you still feel it now? I'll bet you don't because it was not really love. It was you imitating loving behavior in a way that is healthy for small children to do.

The proof of this will come to you years down the road. I've been through this, and I speak from experience. Someday, after you've truly let go of this relationship and gotten some time to recover, you will be very surprised at the change that will come over you. You will find that you forget little things about this guy that you believed you would never, ever forget. In ten years, you will find that you don't remember when his birthday is, or what his middle name is, and other small details that we tend to remember about people who legitimately command a place in our hearts. Those are just examples. Maybe you'll remember those things and forget other things. In any case, you will be amazed at how little space he continues to take up in your mind. You will find yourself amazed that you remember so little of what once seemed so important. It is because this is not really love, IMHO. You have love in your heart that, right now, that you don't know what to do with. So you've given it an object. This guy became like the teddy bear that you used to believe was very dear to you. It's not a real loving relationship. The stuffed animal or doll couldn't love you back and neither can he. Maybe, it's not even his fault, but it is how he is.

How nice that you have this platonic friendship with someone who can give back. Look at how that got crowded out of your life, while you were with the man you lived with. Already, your life is getting more healthy and open to fruitful friendship because you sent away someone who was bad for you. You can expect you're former housemate to keep trying to weasel his way back in. Keep the door of your heart and of your house bolted. Eventually, he will give up. Good luck and know that you've made a healthy decision.