[Serious] Advice needed- I secretly found out my Dad was gay when he asked me to fix his computer.

Several months ago my father said his laptop wasn't connecting to the Internet, and he asked me to look at it. It was pretty easy to fix. Once connected, some pop-ups for Microsoft Outlook showed some explicit email titles.I investigated and found some emails chains with sexually explicit propositions with other males, and that he was on an adult site seeking male companions, with photos of him wearing female lingerie.Here are the family dynamics. He's still married to my Mom. Who is openly against Gay marriage. She's softened up over the years, as I've given her logical reasons on why it's fine and not for her to judge. As I have no issues with anyone being gay.They have 4 children, including me. All grown adults with children of their own. I don't know their opinions on the matter. We're not close.My Dad never seemed gay to me. Always talked about girl's tits or ass. Loved working on cars. Seemed like a blushing teenage boy when he took pics with models at the car shows. I assume he's bi.So, clearly he is in the closet. Should I tell him I know? Say nothing at all? I know he's not happy with my Mom. I just want my parent to be happy. I'm comfortable doing, or not doing, anything that would help them be happier.Any advice is appreciated. Anyone else that was in the closet? Is my Dad struggling?