Can you forgive your boyfriend for a lie?

I've been seeing this guy for 2 years and recently found out exactly how many women he's been with. 50! That was hard to choke down and admittedly makes me feel a little inferior. (I've had a beautiful little girl who left me with some stretch marks) All this made me a little self conscious but also made me rethink a question I asked in the beginning about a certain female/neighborhood mattress. If life was a fairy tale she'd be arch Nemesis. She was my best friend/maid of honor but betrayed me and slept with my child's father/fiancee. That was the end of her in my life. But now I found out my now boyfriend lied and has slept with her. He knew if he told me the truth I wouldn't have given him the time of day. But now I'm confused I love my man but feel so betrayed. Do I trust him or will lie again where he feels it fit? And how the hell do you get over something like this!!!! HELP!