Boyfriend on adult chat cams?

OK so I wasn't looking for it but I went on my BF's search history to find a website that we both use easily instead of typing it and I found out he spent 20 minutes with a live cam girl. Should I be upset? I feel upset. Im fine with porn and fantasy but there's something about a live chat that gets to me. I know he's just gonna get pissed if I bring it up and it's only going to start an argument but IDK I'm just so distraught, I won't be able to hide it. He recently blurted out that his housemate saw him naked and when I tried talking to him about it we argued and he said "it's not a big deal to adults" so I know this isn't going to be something easy to talk about