'Str8' married guys that fuck gay men?!

I don't understand it - if you're straight then why are you fucking gay dudes?I found this book online about gay guys blackmailing straight guys who have sex with gay guys online: http://ift.tt/2nDhPYB it got me thinking..Are you gay? Have you lied to everyone? I checked out a site called Squirt to do some investigating and asked a few questions (via message) and so many guys said they just do it for a release.But in my opinion they'd have to be at least partly gay to get any release, right?