Hi
Grief effects us all differently and I have to say that in each if my 3 break ups with durations 7, 11 and 10 years long, I never really moved on until I found the next lady I fell in love with.
My current wife had our 10 year anniversary last year, I've been the happiest out of all 4 relationships.
In your situation meeting up with your ex with enjoying your child would certainly stir the pot of "regret and what could have been".
Following one breakup I considered going back to her. She was the mother of both our daughters. A friend said "never go backwards as you return to the same fate". So my ex remarried and eventually her husband split from her. He rang me and met up and- he explained he left her for exactly the same reasons eg abuse, manipulation, narcissism etc.
So while regret is hovering it isn't productive. If you still desire a partner don't give up nor settle for less than the best.
Happiness is complex, clouded by the past but the horizon should be your focus.
Repost anytime
TonyWK