I remember when I went through the self-hate stage.
I had problems with my parents, I tried to run away, kill myself.
My parents took me outta school one day and took me to a family crises center, they really helped
After only one visit, I felt a lot better, and I think you will too.
About telling your fiancee and co-workers........
hm.that is a touchy subject, if your fiancee is a kind, caring, understanding person, you could tell her. Make sure it is clear to her that you STILL WANT TO GET MARRIED AND THAT IT HAS NOTHING TO DO WITH HER!!!!!!!!!! Your co-workers, I dunno............
Trust me, go to counseling if it is that bad, they can really help you man
Best wishes, and don't hate yourself, if you be the best person you can be, then there is nothing to hate!