Breakdown in communication

[EmmaRoid]

Separated from the children's father, and he left the family home 2021. As far as separations go, it was ok and we managed to maintain a civil relationship for the children.

He started seeing someone else almost immediately on leaving, however we agreed he wouldn't introduce her "for a while".

Turns out he had been allowing the GF to be with him the recent days he has the children but failed to mention this to me at the time it started.

Is this standard behaviour from an ex - that they do not tell you significant things?

Will comment below this for background.What can I do to both calm down but also to repair things, as I do not trust him not to do something similar in the future however if we can't work in the same direction, the children will be at detriment eventually.

For context -

Previously, he was controlling (took me ages to realise this) and things took a spiral downward into verbal and then physically abusive behaviour towards me -which is what led to the separation, but for the sake of the children we worked out how to co-parent to suit their needs.

I feel like he has purposely limited my ability to support the children which in turn makes me feel he was getting a kick out of knowing what he was doing whilst I was oblivious (something that did happen previously).

I do not expect a running commentary of what they (him and the children) do together as wouldn't want to provide this either, but I am so annoyed something this significant was not mentioned to me. I only found out as the youngest was sick (vomiting) with anxiety and when directly asked what was bothering her said it was because she was "not happy (GF) kisses daddy"

I'm still very much in the period of enjoying getting back to being "me" after so much of "me" was chipped away during the relationship - so my view may be affected, however, I feel I have done nothing but support the children to have a relationship with him - such as encouraging them to see him on the days they rather not etc as I am determined despite everything from before, they will make up their own minds who he is and will not be shaped by my opinion nor feel they have to do anything to avoid hurting my feelings (I want them to have a good relationship with us both).

I can't see why he allowed this situation to happen when all it would have taken was a quick message to say them meeting was happening or would happen.