Oof....that's a rough outlook of us men.
It was months ago, but we were discussing cheating here with regards to its prevalence amongst the sexes, and a study was posted that showed the youngest adult demographic of men and women cheated at about the same rate. I'm not convinced it's a gender thing, but more so a societal thing, in that in years past it's been more acceptable for a man to cheat. The difference in acceptance has dissipated.
I think temptation exists for both sexes, and that temptation can be physical, emotional or both. The second is the more dangerous. Physical lust almost always fades and you can come to your senses and realize what you're doing is wrong. Emotional bonding though is another story, and ties you to the person. That's the whole point of the emotional bonding mechanism in humans. Affairs of the heart are always more dangerous than affairs of the body.
That said, I don't condone either. Maybe that makes me an anomaly as a man, but I find the OP's lack of respect for his wife even more disturbing than his lack of respect for his friend and his friend's wife. I understand forbidden fruit being exciting, and being aroused at the thought, but then to actually whack off in his friend's ensuite bathroom to his friend's wife's undergarments....fucked up.