Dunkan77, I have two things to say. Firstly, don't put all this guilt on yourself, man. I seriously doubt you're the one causing your friends self-harm/suicidal thoughts, so just put that out of your mind. It sounds to me like you're a good friend. The second thing I'd like to say is that you should talk to your school counselor (assuming you're in school) to get advice from a professional, and watch this youtube channel. If you can get past the incessant perkiness of her videos, there is some excellent information and advice on just these sorts of issues.
Oh and three, I would strongly advise against going directly to their parents and telling them the situation. Your friend might see it as a violation of trust and it could backfire in a big way.