Depressedgirl,
You're in such a dark place at the moment, I urge you to talk to someone. If you bottle it up, it will only make the urges to harm yourself stronger. You say you'd prefer not to talk to your fiancee or your mum. I can understand that, but if you tell your fiancee, he may just surprise you. I was speaking to a lady on this site in another thread who said she had been abused in the past and her husband knew nothing about it. When she did tell him, he supported her all the way. Marriage is a partnership and you should be there for one another in good times and bad. Give him a chance to support you. It's better to do that than be forced to lie to him, or hide things from him for the rest of your life.

If you really can't talk to him, is there a work/college councillor you could go to? Maybe your doctor, or someone at a local church? I'm afraid I don't know how it works in the US, so I apologise if this is really bad advice.

Failing that, the people in these forums are amazingly supportive. Putting the things that make you feel like hurting yourself on 'paper' might help you figure out your emotions and help you deal with them.

Try not to blame yourself for what happened to your father. I know it's difficult, but you were not to blame. This blame you feel is entirely normal and anyone would feel it in similar circumstances.

Thinking of you and willing you to be strong,
Astenon