I've been in a relationship with a guy for 3 years. We've always been very close, trust is still something we both work on but I've never worried about him cheating on me or anything. I have 2 daughters, 7 and 3 who live with us.

A few months back I was browsing the history (one habit of mine from a past relationship that I still can't break) and found some porn on there that threw me off. It was a search of "mother daughter brother" that brought up a video I couldn't bring myself to watch. Early on in the relationship my oldest daughter's father accused my current boyfriend of trying to molest my daughter. She had almost never been alone with him, it was nothing but brief, 10 to 20 minutes at best. I felt like it was more my ex and ex's mother who were trying to create a bridge between me and him. We'd only been in the relationship about a year and it took a huge toll on him. He's never mentioned being molested or anything like that to me, and although he plays with my daughters (tickling, play fighting, stuff I've never viewed as inappropriate) I have never had a reason to believe he was at all interested in them.

When I did confront him about the porn, he said it wasn't two people who were related, that was just the search he had to use to find the video, and that it was actually about a younger couple who has a mother figure step in (not literal mother) and... well, move things along, show the younger girl what to do and how to do it.

He's since been very good at hiding any of his porn, and I couldn't bring myself to watch the video before confronting him and really have no way of finding it.

I'm not sure whether I should be worried that he does have fantasies about my daughter/s or just see this as a strange fetish of his and move on.
Help?