That's weird. When I am off, I don't read those messages anyway. Who would be checking at their messages AND be annoyed at receiving them?

I don't know their working hours, we've got staff all over the globe and people work whatever hours they like. I have no expectation for anyone to check work communications outside of their working hours, and it's bonkers to me that people think anyone would have that expectation.

assuming something wrong is fine, even getting upset is ok, feeling hurt, and expressing that is also ok, it's a misunderstanding after all. these things happen. but the next step is to talk about it. what is wrong is to immediately threaten to breakup without finding out what the problem is.

if you are sending me a message that says: answer or i'll delete this chat, which means break up, and i am not even able to see the message, let alone respond, so i have no clue whats going on, then i effectively learn that you don't trust me and that you'll assume the worst whenever something happens. that's a character trait that i can't handle. which means we are not fit to be together.

you are right, as in your other comment that this depends on established communication patterns, and if i know that my partner gets anxious when i don't respond quickly enough then, like you suggest i'd let my partner know in advance. but you could also have a situation where you can't do that. the phone breaks, you get into an accident, or you are so sick or tired that you fall asleep before you have a chance to send a message...

i would not respond with a counter-ultimatum. that's the thing. ultimatums should never be used in a relationship. breaking up is a step i would take after the conversation, if i come to the conclusion that my partner thinks it is ok to threaten me like that. i had a partner do that to me three times over the course of half a year. after the third time i had enough. i realized that this is part of her usual behavior, and she will continue doing that whenever something upsets her to much. she refused counseling too. so i said good bye, we are not fit for each other. i never threatened to leave myself. i tried to find out what is upsetting her and resolve it. i had to realize that this was part of her character and that i would not be able to keep going. i had no motivation to try to change her. that's generally futile anyways.