Hi Ricky2005
Welcome to bpdfamily. I'm sorry what brings you here, what you and your partner are dealing with your young daughter and ex-wife, it's a rollercoaster. I'm glad you've reached out for support, parents here understand, you are not alone. How's your daughter got on with the CAHMS therapy?
You are right if your current approach is not working to change it.
To your right

are tools and lessons that help improve relationships through changing the way we communicate. They do take practice. And at the top of this board you'll find 'Lessons: What a parent can do'.
Have you considered consulting with a qualified BPD therapist for support and guidance with the behaviours you and your partner are dealing with, is that something you'd consider?
Keep posting it really does help.
WDx