i don't blame you for feeling that way.

You spend most of your time making sure everything is ok for your bub.
Then you have to be in the company of your ex and his family, who put you down (in your presence too) and demoralise you.
So even when you're not with them, you know you will see them on a regular basis, due to the shared access, so what a huge amount of stress to you to be continually under.

WIth all of that weighing on you, and being a sole mum, no matter if your RATIONAL mind knows that da da is the first word a child says, it STILL must cut you, to hear it.

i am not at all surprised hearing her say "da da" hurt you. makes perfect sense to me.

hugs to you.