Come on...this does not add up. Most betrayed spouses (BS) on the site, tend to have some sort of a hunch (with less "clues" than you seem to have). Honestly...what does your GUT, your intuition, your heart tell you?
Not to mention probably every single BS on the site can tell you at least one story where the wayward spouse (WS) told them a hundred lies denying the A, got mad or defensive, VEHEMENTLY denied it.
My WH lied to me, several times, lied to our friends, our colleagues, his parents, our pastor, his individual counselor, our marriage counselor, and who knows who else, before I finally found the love letters on the e-mail between them. He even lied to my face days before D-day, when I was expressing my concern with a business trip he was going to take. I did not want him to go (because he had told me the whole "I love you, but I am not IN love with you story" and I asked him not to go. He told me he was definitely going to go, so I made him promise that his trip would not interfere with our marriage counseling, reconciliation, etc...little did I know he was telling me this, making this promise, and he was really going to see her).
Look, it may be well worth doing some further investigating. Does he have a cell phone...check his records. Credit cards, the same. Maybe install spyware on the computer. Hire a PI.
Knowing is the first step to a possible recovery.
But the photos on the computer thing sounds very suspect. And if he is not in an A yet, he is on the superhighway to one real fast. I would read up right away in affair proofing your marriage. And I am pretty sure that women sleeping over in your hotel room or pictures of women you know on your computer are not a good way to keep your marriage safe from infidelity.
Good luck, sorry you are here. We will be here to help you!