My boyfriend has had too many ex'es.

My boyfriend and I have been together for 8 months. 
He's my first actual relationship and I feel really bad because he, on the other hand, has had way, way too many girls in the past. Over 100.
It's true, he's older than me (10 years) but the thought of him having random sex with random people (mostly) over and over bothers me more than it should and I can't seem to be able to get over it. Sometimes I even think to myself: wouldn't I be happier if I left him? 
PERSONALLY, I think sex is something extremely intimate that should definitely not be done randomly.
I try to accept this fact, that he's had so many girlfriends in the past, but so far... I can't.
He says he loves me and claims he wants to spend the rest of his life with me.
I need your opinions and please, take this post seriosuly.