My heart goes out to you.
It's good that you say 99% of the time you're ok.
You must not think that it was your fault, you were not there. Even if you had been there, you probably couldn't have changed anything.
To be honest with you, do you feel guilt over something tangible? If so, it's time to really deal with that guilt and move on. If you have no solid reason to feel guilt, then don't beat yourself up over it.
Suicide of a loved one is an awful thing for anyone for anyone to come to terms with. Those that are 'left behind' feel guilt, and surround themselves with the 'ifs, ands and buts', 'could've, should've stopped it'.
Firstly your girlfriend had a horrific accident and lost her leg. Maybe depression over all of this made her feel the only way out was to take her own life. Maybe she felt it would be better for others. Only those around here at the time may know how she was feeling, but quite often those who do take their own lives can appear to be ok and keep their inner thoughts and feelings to themselves.
It all must have been a terrible shock for you.
You should be able to find Bereavement Councilling in your area. Please seek this out and work through your grieving.
You say you go into 'wild moods' and 'go berserk'. I don't know exactly what you mean by this. Do you hit out at those around you? Have you friends/family who give you understanding?
You will get through this. Believe in yourself. It may take a while. When you think of your girlfriend, try to remember happy times. It is a good thing to cry and let out emotion. Don't bottle things up.
You cannot change the past. That may seem harsh, but it's true. You must begin to look forward to the future, and trust that things will get better.
I hope this will be of some help to you and wish you well.