I'd like to chip in my two coins in this topic.
I am a single guy and i love to swing. Not because I can't get a girl, I am fat, can't get it up, or am there to steal your wife. NO, not at all.
I assure you, I can get girls, I am fit to a degree, and love my hard-on.
BUT WHY THIS LIFESTYLE.
Because I love group sex more then plain vanilla, and I have been slapped many a times, asking a girl if we could get into a threesome. I do it, because that's where my kink lies. so while i am still searching for a lady, who could entertain this idea,
I am single.
Other couples may hate this, and some don't. it doesn't effect me one bit because, I am not desperate. I don't want your wife as my own, all I desire is to fulfill my desires when opportunity knocks. (period).