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Thanks for all the answers and even the interactions some of you have with each other make me smile!
The general consensus seems to be that my g/f is insecure - I agree. Also, I have no interest in my ex wife per se, but if I go to see my son, she will be there so we may as we'll get on, right? I hold no grudges that she had an affair and left me. She respects the fact that I put our son first - the real winner is that he gets s calm balanced upbringing I think.
My ex would happily be invited, but her animosity levels and anger towards the topic preclude that idea from happening sadly - but it could happen for sure
We do not live together. We were going too in June, but she backed out on the day of moving in, citing some minor excuses to delay things. Only now she says this is the real reason! I find her mindset hard to keep up with!