Ex - boundary issues

[Intheair2nite]

I have always had issues with my boundaries and exerting them with my ex. How do I deal with this?
An example being, when he says “I can’t have the kids tomor night because I have to work late” . He doesn’t ask me, nor does he arrange alternative provision. But I just numbly nod my head and go along with it. All of my friends think I have being a mug and letting him get away with out, but I can’t cope with the anxiety of standing up for myself with him.

Anyone being through similar?

Anyone?

Do you have the same flexibility with your time? I'm assuming not.

How often does this happen?
What if you have plans for while he has the kids, do you just cancel them?

To be honest, if he can't have the children due to work then he can't have them. If you will be home then why would he arrange alternative childcare. You are their mother. If he can't have them then you should?
Does he rearrange the date or does he just cancel. Next time he does this, say yea I can tonight but they are with you on Wednesday etc instead!

Do you have a custody schedule?

Not being funny but I often hear people say “it’s his time he needs to arrange alternative child care” but how exactly would anyone enforce that? Surely your ex just won’t turn up? Not much you can do about it unfortunately as annoying as it may be.