Sending you a virtual hand to hold. You sound fun, capable and strong. And a great mum.
Must be incredibly painful for you as both a partner and a mother (how can a parent move 300 miles away from their child?)
100% agree with others don’t trust him to honour his proposals/behave reasonably about how you’ll handle the split. He’s proved more than once he’s not to be trusted. I speak from personal experience.
Move to communicating by email (where at all possible) or messaging, rather than verbally. That way you’ll have a written record of everything, including his reason for leaving and any guilt-ridden empty promises he makes over the house etc, which may help in a final settlement (though I’m no expert).
IMHO you’re best shot of him. Shagged someone else on his stag do. Contributed nothing to house deposit or mortgage, yet happy to have house in his name. Using a car you bought for him. Leaving you and his child for a woman he’s supposedly never met IRL and only known for weeks. What a disrespectful, freeloading, fickle a-hole/conman. Clearly no integrity.
If the new woman lives near his family, could she be an old flame and the Tik Tok business is a smokescreen?
You’re doing the right thing trying to remain civil and calm towards him (while being secretly hardball in fighting for as much as you can). First, this is best for your child, who needs to see mature behaviour modelled, esp if he’s dealing with trauma. Second, it’s more likely to get you the outcome you want in terms of your home etc.
Finally, are there any other men in your son’s life who could be there in person for him when his dad moves away? My sons really lacked this (no grandpa, uncles etc) and it’s been tough. When they get to secondary school, they grow up fast and (however good your relationship) having men to role model, talk to and take an interest in them as a teenager/young adult really helps.
You’ve got this.