Caught My Partner Looking at Porn Together

I've been in an open relationship with my partner for about a year now. We agreed that we can explore and be honest about our desires, but there's something I haven't told anyone yet, not even him. Last week, while he was out, I found some porn on his computer that really made me uncomfortable. It wasn’t anything illegal or extreme, just stuff I didn't feel comfortable with seeing together. But here's the thing: a few days later, I accidentally walked in on him watching it on our shared device. We've never done something like that together before, and suddenly it felt weird and almost dirty. Should I bring this up to him? Is it too late to be honest about my boundaries now? Am I overthinking everything?