I am very sorry for your pain. It sounds to me like this man has a serious mental illness. I have posted a link here for you.
http://bpdfamily.com/
Cutting is a hallmark of borderline personality disorder, as is addiction and the general 'victim' mentality. I'm not saying this is his problem, just that some of the information you may find here may help you. I am not trying to be cruel, just realistic.
It seems to me that you are taking way too much responsibility for the mess this man's life is in. You are not God and you cannot save him from himself. Why do you feel like you owe him your life?
What about YOU? YOUR life? YOUR health?
You are not married, you are not family. Why is that you think all this is somehow your fault and you are the only one who can help him? Is that what he tells you?
IF he does indeed have MRSA, he is putting you in very real danger. Why is that OK with you?