AMoonHawk saiddoes he have a job?
He said it's his co-worker!
First and foremost, I'm really sorry to hear about that; situations like these are always so upsetting. Anyone who has ever caught their SO in a cheating-situation knows what that feeling is like to literately lose your breath over the ensuring whirlwind of emotions surging through your brain at once. In other words, it's crap.
I've been through a similar situation with an ex somewhat recently (which creating a thread about it on this site is what actually lead to me participating and maintaining an active profile). Finding out the extent of the "questionable exchanges" is the hardest part - you may be reading one thing but hearing another. The conclusion that I've reached on that was that I really didn't need to know.
What I mean by that is to trust your instincts and your intuition. Do you think the extent of these messages were just 'harmless' fun or do you think your bf actually had the intention of acting on these exchanges, assuming he hasn't already?
What are your impressions of discovering that after a month, your boyfriend tells you that he loves you... but you also find he's been talking to other guys? Put yourself in third person and answer that question.
People make mistakes. Perhaps he didn't know where the boundaries were exactly and he was just 'toying' with people. However, in my honest opinion, finding this only after a month of commitment is only a preview of what is to come.
I dont know him or you, though, you may find that this is something that you guys could work through and that this issue is trivial compared to what you guys share. It's really a decision that you have to make.
Either way, I wish you luck.