Just wanted to wish you well before your thread leaves for a more tailored board.
You are right to prioritise the safety of your child and yourself.
OneEpisode above gives some good, practical advice at how you can do that within the law (always best for long term, even if it feels counterintuitive/emotionally wrong in the short term).
From an older (and hopefully now wiser than in my younger days!) no man is worth this level of drama. You and your son will be much happier without all this unnecessary angst in your day to day, and disinterested fathers tend to drop off the access radar, if you ‘grey rock’ and don’t let them see how much their fuckery upsets you.
For what it’s worth, I have never known a woman who regrets minimising contact with a baby father (and regretful feelings at ever getting caught up in a dickhead’s orbit are offset by love for your child).
Minimise all encounters and seek support to organise only supervised contact between ex and child if you have even the slightly safety concern.
Don’t badmouth ex to child (or mother of half siblings), just make your boundaries clear ‘it didn’t work out and never wiil’ and reassure the child ‘I am so glad you exist in the world’. When your child is going old enough to recognise your exes failings the self, then you can be more open about it, but always keep your revelations age-appropriate, which might well mean keeping some things back until your child is well into adulthood.
This doesn’t mean pretending your ex is a better person than they are though. It’s a fine line to walk, but you can do it, with support.
Contact the Freedom programme for support and ‘reset’ so that future relationships can be healthier. We have often pick partners who are bad for us and learning a bit about why and how are they’d to your own freedom.
You can get through this. Millions of women have, we are all rooting for you, don’t get pulled down the drain with your ex and his ex (and she needs to do the Freedom Programme as well, frankly).
www.freedomprogramme.co.uk/
Relationships or legal will give you more practical answers than Feminism, but you ate always welcome here. Feminist discourse is a great stepping stone to personal freedom, although perhaps less helpful in this moment.