I don't know what to do here. Parent problems.

First of all, I think this is a severe intrusion of your dad´s privacy. Checking browser histories and the kind of sites he was on - why all this paranoia? Has he cheated before? What next - checking the phone numbers he has called? Hiring a detective?

I mean, maybe I just don´t know enough about the situation. I heard something similar before. He never wanted to have sex with his partner, but was happily watching porn and masturbating. Well, while I understand the thinking behind it, I can´t follow it. It´s along this ancienct cliché of total monopol over the partners sexuality in a relationship.

And if your dad is really homosexual - well. Then he´s been hiding a part of his identity for a long time. That brings you in a conflict. You want your parents to stay together, most children do, as this was their base for surviving the helpless years if childhood. But don´t you also want your dad to be happy and to be able to express his true feelings, his true sexuality? Tough situation.

Jam it back in, in the dark.