@PithyBeaker
You speak of love, and of the fact that he's 'not a monster'.
I'm old and I've seen and done a lot! So take this from me; there are times when love is simply not enough. And when a person isn't 'bad' or 'a monster', they just aren't right for you. This is one of those times.
You can love someone to distraction and they could even be a prince among men, but that doesn't mean that it will be a 'happily ever after'. There are just some problems that are insurmountable.
And his attitude and behaviour towards you and towards your son (being in his own home 'too much') are exactly that, insurmountable. You can't change someone who doesn't think they need to change, who truly thinks they are in the right. And who wants his wants and welfare to be at the very centre of every decision you make. And that certainly does NOT make him a prince among men!
Also, if you haven't please look up the sunk costs fallacy. It doesn't matter if it's been 5 years or 50 years, there is no point in staying in a bad relationship.
I'm glad you plan on speaking to him on Friday. But remember, you aren't asking, you're telling. And that you will not hesitate to 'get official' if he doesn't agree to leave. Remember that he has a LOT more to lose by being nasty than you do.
And please don't give him an inordinate amount of time to wear you down get out. He doesn't need more than a few days to get out. FWIW when I decided that DH wasn't going to stop drinking, I managed to get my things out of the house and moved into storage, find a flat, and then get my things moved from storage to there all within 72 hours. And your DP already has a flat to take his things to!
I don't know your schedule, but I'd suggest having 'the talk' at the beginning of the week he does NOT have his DC. That way there will be no excuse for him not to get gone ASAP. He can get out in 3-4 days and still have 3-4 days to set up the flat, even less needed to set up if the flat still has his furniture in it. Remember, it only took me 3 days to get my things in my new place.