my partner and i are poly. we broke up for a while and got back together. while we were apart she acquired a partner that she didn’t tell me about. the betrayal makes me uncomfortable now that i’ve found out (months later) and my condition for staying in a relationship with her is that she stop this relationship with the other person until i’m comfortable with it. she says i’m being unreasonable and leaving her with a hard choice. I have a hard time not saying tough titties. am i being crazy?

This is a tricky one. When people are broken up, they don’t have any obligations to the other person (beyond the obligations we have to be decent to all people). But once you got back together, if she still didn’t tell you about this new partner immediately, that’s a problem.

Situations like this are one reason why clarity about the terms of your relationship is so key. If you two had clearly established an arrangement where you’d be open with each other about who else you were seeing, this is a betrayal akin to cheating in a monogamous relationship. But if you never explicitly said that keeping another partner a secret wasn’t okay, things get trickier - at least from her perspective.

That said, I’m of the opinion that keeping something secret makes it inherently not kosher. Lying, lying by omission, hiding, sneaking, etc. have zero place in healthy relationships. And you are totally within your rights to feel uncomfortable with this. I think your demand is very reasonable - taking a mulligan on that relationship and letting you have some time to get comfortable with it like you wish you’d had the opportunity to do the first time around.

But even if I didn’t agree, or just because someone else wouldn’t feel the same way in your situation, that wouldn’t mean you’re “crazy.” You are totally entitled to your feelings, and you have a right to set terms for relationships that are healthy for you. If you’re uncomfortable with something, don’t stand for it. 

My advice is to stick to your guns. You’ve set a clear boundary with your partner. She can choose to honor it and work things out with you, or she can decide not to. That’s on her - it’s not a reflection of whether you’re “crazy” or not.