I went on a boat cruise with a mate and his girlfriend of 5 years, we all hit the piss badly and my mate decided to pike it to bed early. During the next few hours on the boat cruise I see her getting it on with another bloke and my mate was sleeping at the time. I always suspected her of being a cheating bitch and my mate wouldn't believe me as I had seen a few strange things before. This time I woke him up, he seen her all over this bloke and didn't even flinch at what he had just seen and went back to bed, to which I thought at the time was a bit strange.
The next day he just acted like everything was normal, no arguments and nothing was said. They drove me back to their place after the cruise as I had left my car there, everything still seemed fine, I go to jump in my car and realised I had left my keys in the house. I go back up to the house and catch my mate swinging her into a wall by her hair. I stoped and look as I was speechless, he then turned around and just apologised that he was sorry that I had seen that. I then decided to hang around for a few hours and everything went calm. I then asked if she was OK and she said "yes", I asked if she wanted a lift anywhere and she said "no". I just left at that, went back the next day and she looked fine, no black eyes, no bruises on her body that I could see. They still continued to see each other for another two years and then parted their own ways.