Weird or just fantasy?

I've been with my partner 9 years and for as long as I can remember whenever I have managed to log into the computer I always see nude celeb forums pop up or pictures of the same celeb girl each the moment he's got a thing about jojo the singer he just looks at loads of pics of her and also Emma used to be Chanelle Hayes from Big Brother who he had lots of pics of....I used to find it harmless and just one of his fantasies...he'd never be a stalker or anything like that he's far too laid back...he says he's a very visual guy and likes looking at good looking girls/celebs which is what all men do as it is only natural but when I see it happening nearly everyday should I be worried? I mean I do get jealous I am only human and I know he'd never meet these girls in real life but sometimes it does freak me out, what do you girls think? Oh I did also find pics of my sister on his computer at one point about 3 years ago too that he'd masturbated over and I was about to split up with him because of it but he insisted that it was just fantasy and he doesn't fancy her or anything like that am I being too lenient?