So he initially lied to you about it -- then later admitted that he thought she was hot & looked five times....

What also sticks out to me is that he looked at porn right after --- so was he turned on by your sister and then had to, well you know, pleasure himself after looking at her photos?!? It's the unthinkable.... but that's what comes to mind through your story. EW.

Can you ask him more questions about it? Problem is, it was a year ago that this happened.

Personally, I would have a very hard time if my long-term boyfriend was looking at nudes of my sister, thinking she was hot and possibly getting turned on by them. He didn't need to go into the website at all since it was password protected, so clearly he was curious. AND the fact that he looked five times??

I don't know, my dear. The ball is in your court. I could never get past something like that myself. He did disrespect both you and your sister. I know my own boyfriend would never do such a thing to me, and he says he loves me more than anything.

And then there's the fact that you don't fully trust him to begin with.... it's the lack of trust that made you want to go into his phone. And rejecting you sexually? This doesn't sound like it's going in the right direction.

Erebos laid out some options for you, which I think are helpful. Perhaps couples counseling would help you to decide whether you can move forward or not.