In college there was a guy who served as co-president of the Gay-Straight Alliance. He had a boyfriend and was an active gay activist. But apparently he met a girl and they started fooling around. I don't know if they went all the way, but he told me that he'd made out with her and that she'd sucked his cock on a few occasions. He felt guilty about it so he confessed to his boyfriend, who was pretty pissed. Eventually they broke up. I haven't heard anything about the guy in years, so I don't know anything else.
 
What makes someone cheat, that's a tough question to answer. I think it depends on the person. Usually it is an indicator that something is lacking within themselves and they are completely fulfilled within their relationship. If someone cheats it's because of their own issues they are dealing with not their spouse/partners. Unfortunately it then would be up to the spouse to determine the outcome best for their circumstance. I think it very odd though that someone who proclaims themselves as gay would cheat with a women. I wonder what the circumstance was were they drunk, on drugs?

Hugs, tugs and rubs