I (24mtf) have hooked up with this man (35m) a few times over since the beginning of summer, and tonight after hooking up he confirmed that he had a GF, and they they had an open relationship.

We had already hooked up and in the past he has teased me about having a GF, and when I would say "no you don't" he would laugh and take it back. Tonight he teased me the normal amount, but I kept pressing, and he showed me many recent pictures of him and a girl. I shut down in the car because I felt I was the instrument of his infidelity, but he said he has an open relationship/ethical nonmonogamy thing with her.

I felt really weird that he didn't tell me other than the teasing, but he said it was normal in this kind of arrangement to not disclose that before hooking up. But I feel confused and like a secret was kept from me in order to get with me. I've only ever dated monogamous and have no ideas what the rules and etiquette are, but am I crazy to think that I should have known I was inserting myself into that sort of situation before we hooked up multiple times over the course of 6 months?

To be clear, I probably would have still hooked up with if I knew outright, but it feels like an oversight on his part in the process of mutual consent,, or like he's just cheating.

pls help I cryinf :(