Is it stupid to leave a relationship over something that happened a while ago?

So about 2 1/2 years ago I got one of those feelings you get when you know something isn't right. Out of curiosity I did some snooping and found on my bfs computer history a ton of porn and saw he stalked photos of a co-worker of his and it's easy to put 2 and 2 together. I didn't bring it up, I stayed quiet and found that he did it a few more times after that. I finally brought it up about a year ago, in tears, and he got all defensive. I haven't brought it up since and as far as I know of he doesn't use Facebook anymore. What I wanna know is, is it ridiculous for me to leave at this point because of it since it was so long ago? It still hurts me to think about but I feel like I may be overreacting. I don't know why I haven't already left :/

I'd like to remain anonymous so I'll just answer here. There were over 100 pages of porn and he had viewed all of her bikini and summer pictures and after I finally confronted him about it he had admitted to getting off to her pics. I know people say porn is just porn but he is always sneaky about it and closing out of it the second I walked in the room even though I had previously told him I didn't mind.