All good advice this week but your math is way off. An extra partner doesn't mean 33% more chances of drama, but 350% (if we value everything as equally probable of causing trouble, AND if you neglect the real complications).

Look at it: Two partners means two relations (at face value), namely me from your viewpoint and you from mine. There could be a little jealousy (in the mild form of 'he/she's better looking than me'), and there's always some friction (I/you want want more or different stuff), etc., but that's about it. Draw it as two dots representing the partners and an arrow going from each to the other.

However, with three partners it goes from two to six relations, not three (so 3x as much, or +200%, not +33.33...%)—namely the two relations between every pair within the triplet. Draw the three partners as three corners of a triangle, and the relations as the six arrows from the any to any other point. Plus for each of the three, how they feel when they're all together (assuming they're meeting regularly, socially, not just for sorting out their triangle issues). So that's an additional +150%.

Realistically speaking, however, there's a further three relations: Each one will have feelings about the relation between the other two, right? And this is where the "real" source of longer-term trouble lies: when one feels threatened that the other two get along "too well" and winds up feeling excluded. So draw a little ellipse around each two points, and an arrow from that ellipse to the remaining point. I don't wan't to add these to the earlier sum, because they're different types of relations (apples + oranges = ?); mostly, I'd say they're heavier-weighing if they're negative because it's all second-guessing about what goes on when you're not present. And, if positive, those feeling are unlikely to have a strong positive influence. So count one of those ellipse-arrows for two of the earlier, or three, maybe? A "magic" made-up number (2? 3? other?)—a sure sign you should stop counting.

Actually, it has been said that whenever there's two people in a room, there's six people present; the people they think they are, the people they think the others are, and the people they actually are. Adding a third person in that room is left as an exercise for the reader.

All The Best

P.S. I knew that applied maths PhD would one day prove its worth.

Thanks for sharing, ATB! Another letter from a mathletic reader... after the jump...

Hey, Dan! Reader since '02. Enjoy the column. Married since '96 and now find myself saving columns for my kids to read as they enter their teens. Thank you! But regarding this in your latest column...
The addition of a third person may mean a 33 percent greater chance of someone feeling awkward after the three-way is over, and that isn’t awesome. But there is a 100 percent chance of having a three-way, TPV, and that is awesome.

My wife and I have often talked about how much more complicated a household gets if add a kid, grandma, or any other person with freewill into the mix. We gained some insight that I thought I would share, as it gives us some context. Our realization came from reaching back to grade nine math and "factorials." The number of individual relationships in a group is the number of people, factorial, or "N."

One person? 1!=1 so there is just one relationship. Mine, with me.

Two people? 2!=2*1=2. Two relationships. My relationship with you, your relationship with me. To buy IMO this of course you have to believe that my relationship with you is a distinct thing from yours with me. I think that's true.

Add a third? 3!=3*2*1=6. That's right. Six distinct relationships:
A with B
A with C
B with A
B with C
C with A
C with B

So is adding a third more complex? You bet. Triple, not 33% more.

However triple complexity doesn't mean certainty of a problem, and your 100% stat is right on the money!

S.B.