<human>: I'll try to keep this short. 

My boyfriend [23/m] and I [21/f] got together last September during the beginning of semester at university. He was a transfer student from a different school.

Last night I wanted my BF to meet my two best friends. I've been meaning for him to do so, but he was at an internship over winter break. We finally set up time for all of us to get together. 

When I introduced them, I found out that they all know each other, but through separate occasions (we live in the same area. I never met my SO in the area before college, big coincidence). He had to leave a bit early for sleep today for work. After he left, both girls told me that they had slept with him, but on separate occasions. They did not know about this until today that they slept with the same guy. Now I'm sleeping with the same guy they slept with at one point. So I'm a bit pissed at this, but I feel I shouldn't be; I didn't know him. 

I confronted him about it earlier today. He explained that he hooked up with both of them the summer before school, and in the same week. I asked him why he never told me this, and he said that sexual history isn't important and he didn't know that I knew them. I got kinda pissed and went off on him. He hung up on me and texted me saying he'll talk to me when I'm more sane. Now I'm even more pissed at him. 

I dunno, I feel lied to he didn't tell me this, despite that he didn't know I was friends with them. We haven't talked since this afternoon. I dunno how to approach this. I know I should let it go, but it's eating me up, and it's irrational of me, I know. What would you guys do in my situation?

Could you distill the essence of the text into 1-3 sentences?
<bot>: Me and two of my best friends slept with the guy I'm currently dating at one point; no one was the wiser.