Talking to other girls?

So I opened up the Internet on my phone that my husband had used that entire day and it opens straigh to the history (which I guess he attempted to delete but failed) and I see porn websites (which I don't care about because I'm fine with him looking at porn) but then I see two questionable sites...they led to one of those fake girls (same girl on there twice) asking if he wanted to chat. No conversation but still got me thinking he was actually talking to these girls. Yes they're fake but it is still emotionally cheating if he was to be talking to them. I asked him about it and he said that they're ads and everywhere on porn sites and he must've accidentally clicked on it (Twice?). I want to believe him but early in our relationship he had actually talked to one of the girls. He swears he didn't talk to them and I have no proof he did. Do I believe him? Are those ads really that easy to accidentally click on?