Swinging and cheating is so common now...I cannot comprehend for the life of me,how can these people bear watching their wife getting fucked by someone else?!

As someone who has spent some time in those lifestyles, its really very simple to answer. It comes with the territory -- its part of the deal. You don't go to swingers clubs and swing and expect your woman to just sit there crying in the corner, while you fuck as many women as you want, do you? If you can't handle watching your woman have sex with other men (and control your jealousy) , then you have absolutely no business being a swinger. She has to watch you have sex with other women, so fair is fair. Jealousy is natural but you can learn to transform that negativity, into being happy for her having pleasure, the exactly same way you would expect her to be able to happy for you, if you are having fun fucking another woman. It is not for the faint of heart.