My step son’s Mother has been coaching him to dislike me

Mostly because I parent differently from her

This weekend a situation occurred and my spouse and ex had a meeting where they spoke of me and made assumptions that were very untrue
This has all happened one week before our wedding plans
I know what’s in my heart and how I’ve treated this child as one of my own since I’ve been in his life for last 4 years….
But now I am broken by some of the things I’ve heard.
My spouse kind of supported me but did not handle this situation at all in my best interest.
I also suffer from depression, anxiety, ptsd…. And I’m really having trouble
I’d summed up a lot of details but this is the most important ones I guess

This also isn’t the first time she’s done this with me
But this is the worst time

I’m supposed to meet w her and speak about all of this in a few days and I’m having trouble not being completely hurt and irate

Any suggestions-on how I can handle this situation, esp while dealing w my mental health disorders
I feel really triggered