My partner deserted us when my daughter was 4, inevitably he moved in with THING and inevitably the access visits involved little one meeting THING. It hurt me, ...........

Now 25 years later little one, doesnt like him or THING and has worked it out

I know this is a short reply, go with it....... dont bad mouth your ex or her; in time things will work out okay
hide your jealousy and resentment.

Another warning is if and when they do meet him and her they may "play up" by being naughty, just roll with it
anyways Im here if you want someone to talk to xx