Awww, look... No offense, but you kind of got yourself into this situation when you agreed to start seeing him, didn't you?  Or was it a case of you were not told about the boyfriend before hand?  In that case- I think you should drop him like a hot potato.  He's being an ass and you definitely deserve better than that.  You should never, ever have to put yourself in the position of being the "bit on the side."  Find someone who will treat you right!  As for why all men are bast*rds... I don't think they all are, but a lot of them just don't think before they go ahead and do things.