Why doesn't he believe me?

Me and my ex were together for almost 3 years... We were going out for about 6 months when I cheated on him... But then I was so young and didnt know what love was and.. But when I started having really big feelings for him and I fell in love with him, he found out!
Now he hates and despises me, he wont forgive me... When he knows im sorry...
Why wont he believe me and forgive and forget?
It hurts so bad...because I love him so much!
And I know he feels the same way!
What should I do? Its hard to live everyday when hes on my mind constintley!
I cry almost everyday and am depressed all the time... Please help me!

Nothing to help you with. You did the deed, you'll be living with it for a while. Besides, you must have not been feeling too depressed when you were cheating.