help?

Jay
So my boyfriend has slept with over 30 people so whenever we talk about previous sexual partners I tend to get upset because of how many partners he has had. He had asked me who the last person I had slept with before him was, and I told him straight away. But when I asked him he told me it was his ex, then another time he told me it was another girl, and then recently he has said it was another girl?! 
I understand that he has had previous sexual partners, but the fact that he cannot remember which order he slept with these girls in, or that he's just lying to me about it? 
As he had said I was the only girl he'd slept with in the bed he has now, then he has now said that he's slept with two other girls? 
It just makes me uncomfortable and I don't know how to get over it.