is having an open marriage (sexually) a sin?

no, I don't care what consenting adults do to get their freak on

In all honesty it probably isn't smart. I mean, if there's one thing I've learned from a zillion hours of watching Jerry Springer, it's that not too many people can handle such relationships.

"if they both love each other and this makes them happy so what?"

Well that wasn't your question. Who you sleep with is no ones business, but if you're asking if its okay to do so according to your religion, its not.

Adultery is a sin.

People are not supposed to make them selves happy according to good old god believers, they say we are here to make imaginary god happy!!! HAHAHAHA So how do you make an omni delusion happy!!!

How is it a sin? Abraham did it with their maid, after Sarah blessed it.

Yes.

The Bible says to keep the marriage bed pure, that you belong to your spouse & he/she belongs to you, and that lusting after someone other than your spouse is adultery.

Yes, why are you even married.

There is no such thing as sin.

yep