I'm a guy so I'll speak from a guy's instinct and view.
Leave him! ur bf is cheating on u like a runaway train headed for alabama.
Check his hp la!(DEMAND IT!)
Check his icq msgs(pretend to use his pc for some work or stuff).
After u find out he has been cheating(which he definitely has), take revenge! Nothing beats sweet revenge on playboys and 2 timers.
Methods of revenge:-
1) Sabotage his pc by PERMANENTLY deleting some critical system or work related files(a guy's pc is one of his most precious things-trust me)
2) Take money from his wallet(I'd like to think of it as compensation)
3) SPEAD the word that he is 2 timing u but make it look piiful for u.
Tell all ur friends and his friends and all those in the forum. A photo would be nice.
4) After all that has been done, make a big scene and slap him REAL HARD then leave him forever!
If I can come up wif more I'll let u noe.
REMEMBER, DON'T BE SOFTHEARTED! He will make use of it to make u forgive him!!! LEAVE HIM AND NEVER THINK OF HIM AGAIN.
Trust me.