Why does ex do this?

[exproblemsforever]

We split 4 years ago, and since then it’s been a struggle to put boundaries in place as I have to constantly be on my guard as he’ll always try to cross my boundaries. We have tried and have been very friendly for the kids.
However, every time I enforce the rules again and am strict about it, he acts like a little wounded child. At pick up or drop off times he won’t look me in the eye. Won’t acknowledge any handover conversation. Ignores me pretty much completely.
I know he plays the victim as my eldest (9) often says she feels sorry for him.
But just so I can draw a line under this, why does he act like this? When previously we’ve always said how important it is to be amicable. Then he goes to the other extreme because I spell out (again) the boundaries. Argh.

He’s trying to manipulate you. Don’t give him any headspace; ignore behaviour like this.

I guess so. But for what, so that I back down on the boundaries? By making me feel so uncomfortable I let him get away with what he wants?

Practice phrases to say.
When the children are collected have them ready so it’s on the doorstep , not inside your home. Be cheery, have a lovely time dc, see you later/ tomorrow/ Sunday. When dropped back Say bye dc, then you can tell me what you’ve been doing, bet you’ve had a great time. Bye ex. My rules for dealing with my ex were : always be cheerful, upbeat. Always look busy. Never let him inside the house, that’s my space, drop offs and collections always at the door.
Be firm and lead.