Welcome Genoh555. It's good that you're writing here about this. There are some great people here. I went crazy after my GF left me less than two weeks ago in way that was absolutely shocking to me. My family thought I was irrational and almost had me committed to the hospital. I really was a suicide risk, I think. Writing on here has really helped, even if I don't think anyone reads my long posts. But trust me people are reading, and we hear you.
What can I say, you have had a lot of problems accumulate while you are young. You need to really understand and tell yourself over and over that you can rise above this crap. We are for the most part responsible for our lives, but there was nothing you could do about your knee or your Father's cancer. I think that it was humanly possible to fix the thing with your girl, but if you could figure it out you could make a billion dollars in a book deal. Don't pay too much attention to my advice, though, I am still pretty screwed up myself.
Hitting that guy was very, very stupid and totally understandable. Go to Disney and throw his teeth into the water at "It's a Small World."