Boyfriend let another couple have sex in his bed

I don't know if I'm overreacting here. My boyfriend just moved to his first postgrad apartment and it has since become the place to be for his entire friend group. I spend a lot of time there but he comes to visit me as well (we live about 2 hours away now, so we spend a couple of days together switching on and off between locations).

Anyway, while he was away visiting me at my house, one of his friends had sex with a girl he has been hooking up with in his bed. I don't know whether my boyfriend okay'ed it before hand. Yes, the is the same bed that we sleep in (and have sex in).

I only found out a day or two ago secondhand, and my boyfriend told me he initially wasn't going to tell me because he knew I wouldn't like that, which is correct. I don't like that he wasn't going to tell me either. He told me his friend cleaned the sheets but I'm not sure whether I believe that, and it's still disgusting to me. I've stayed at his place the past two nights and I keep thinking about it.

Am I overreacting here? It's not my bed or my apartment so not my choice to make, but it's just nasty imo. We're 22 if it matters.