tldr; im (23nb) a secondary partner, and they (27nb) have a primary NP (who doesnt like me but we've managed to not hate each others guts anymore).

i see them every other Saturday when they spend the day at my house and leave at night. we do also see each other at work and sometimes spend time in a voice call together.

saturday night they tell me around 830 they planned to leave at 9. i was thinking more like 10 (when they more usually leave), and i got mildly upset about this (not at them - just sad/a little pouty). they got quiet and just held me and then, for totally innocuous reasons, i got triggered pretty bad (i have ptsd/trauma from some relationship and sex stuff).

this spiraled into a bad breakdown where i was sobbing, shaking, trying to hurt myself, etc. they didnt ask what was wrong, mostly kept trying to hold me, and after a bit basically said they still had to leave. ended up leaving slightly after 9 with me still sobbing and shaking and overall having a very bad time.

theyve said since they normally dont have a hard cutoff time, but did that night. they didnt tell me ahead of time. im feeling extremely upset and hurt still. i am very careful about never cutting into their time w their NP bc of past issues in that regard, and i feel extremely let down that i was left like that without much explanation or without being given a heads up beforehand, and esp so given theyve cancelled plans with me before bc NP was having similar mental health issues.

this doesnt happen frequently at all. am i out of line for feeling really really upset about this? i was extremely scared and freaking out really badly, to the point they were teary eyed about leaving... but they still did. and after the fact dont seem to know how to make it up to me. i dont know either.

our relationship is otherwise good and theyre my best friend, but i am struggling with what to do now. i really feel like my trust in them has been hurt.