Should I let him know?

I got on my boyfriends myspace, and he does not know i have the password. I found some messages where he had been talking to one of his ex girlfriends. She was asking him if he was married and he said no, but he failed to tell her that hes engaged. Then he went on to ask her if shes married. Do you think this is innocent or is do you think i should be worried? If something is going on how do I let him know that I know about it, without giving away that i know his password? yes, i know i shouldnt be looking at his personal things, but i had suspensions of something. We have been together 3 years. Help please!