Cheating is an act of lying, deception, fraud, trickery, imposture, or imposition. Cheating characteristically is employed to create an unfair advantage, usually in one's own interest, and often at the expense of others (so wikipedia says)

3some is open and honest and in the interest of all involved

So really they are 2 totally different things.. unless of course there is no marriage or an open marriage..

My wife and I talked about this one night. In my opinion it would be hot to watch another man having sex with my wife, but it would be horrible walking in on it if I didn't know what was going on. The two things are really miles apart in my opinion. A threesome is something you do together. Cheating is a selfish act by one person.

*sadly shaking my head*

Look, if you want to swing and get into alternative play, just say so. Have the courage to ask your spouse. Cheating, pfft- the word is adultery.

The difference between adultery and alternative play is the difference between betrayal and consent.

In one, the woman is part of the decision; in the other, an unknowing victim.

As well, with a threesum/moresum, you can set boundaries, and generally there isn't emotional involvement.

Oh, I don't know. I'm rather fond of the fellows I more-some with.
Friends with benefits, dontcha know.

True, but emotional involvement of the jealous type.

It can happen, of course, but that does rather say nothing good about a person - getting jealous.