Once a cheater, always a cheater.. so if my BF cheats, its BYE BYE..
no 2nd chance cos once you break my trust, you wont get it back..

sad yes, but it is better than always thinking or wondering if he will cheat again..
i cannot keep wondering if he will cheat again or not.. sure he may assure you that he will not do it again and to ask you to trust him.. but its just not the same anymore..
its like having a white blouse and you kena curry on it.. even if wash and bleach, sure got stain ..

if you decide to forgive, then dont keep wondering.. i may forgive him but i cannot promise that i can stop wondering..

i may sound very cruel, but that is me anyway.. other ppl might not agree with me..

from my experience, guys DO change... sometimes, guys just 'drift away' unknowingly and unintentionally. they might not even have the intention to cheat on you in the first place. they probably think, hey, this is just getting to know/help a new friend.. what guys dont realise is that if one of them (your bf and 'new friend') oversteps the boundary of FRIEND, it's equivalent to cheating already.

Note the progression: strangers -> friend -> flirting (online or otherwise) -> talking on phone/msn everyday -> meeting up -> more flirting and talking on phone/msn -> doing 'cyber' -> actual physical s**
(note: this is from my life experience and does not apply to all guys/situation)

dont get me wrong, i am not against my bf making new friends.. guys think that flirting is harmless. but flirting can lead to the above progression..

fyi-i had taken the same path as you some time back and i know its not easy. but i have my reasons on why i stayed. i told him that if the situation were different, its over. but once you have decided to stay with him, do concentrate on why you guys hooked up in the first place. can you see a future together? if yes, then the cheating must be a thing of the past. also, your bf must make the effort to gain back your trust.. perhaps, it is an uphill task for him but you must also try to trust him again..

all the best my fren..