Does it matter to you how many sexual partners your current lover has had before you?

I've been seeing a guy for a little over a year now and he's ready to make us official but I'm afraid to get in a relationship because he's told me that he's slept with over 40 women and I have only slept with 2 people in my 21 years (he's 24). He's admitted that in a few of his past relationships that he's cheated numerous times but that he promises he's over that and just wants to be a one woman guy now. I sang to believe him but I just don't know how.