@forfarhill as kindly as possible, why did you post on Mumsnet, because even though nearly everyone has pointed out that he isn't going to change, and that he does not respect you, and sadly he doesn't love you either, you just keep on giving the same response? Please do not take his lack of caring about you, personally, I don't think that at this stage in his life he would, or even could love anyone other than himself. This is not about you or your baby, it is not your fault OP.
You have actually probably been far too reasonable and accommodating with him (so if there has been any fault on your side then there it is). I think that in the last decade or so, young people (and increasingly, more people of my generation - in our 60s) have had all these accusations flying about, calling people 'narcissistic', 'controlling, accusing them of not treating their partners as individuals, who even though they agreed to be in a partnership with the other partner, and even though they may have agreed to have a baby with their partner, they must still be treated as a completely seperate person - to me, on this occassion at least, a completely seperate entity, fills the description far more accurately.
Actually, scrap my last thought please, as having thought about it for another 0.5% of a second, the term/description that fits your 'fiancé' to a T is 'nonentity', to me, your 'partner' is a prime example of a nonentity. I am also questioning myself for having referred to the father of your child as your 'partner', I think I will just Google that term...
Ok, I Googled it, and my own understanding of the word "partner" in a romantic, or at least sexual way, is actually wrong. The term "partner" in that type of situation does appear to just mean someone you share an intimate (sexual) relationship with. Whereas to me, being in an intimate partnersip with someone is about so much more than just having sex with another person. It is about sharing common goals and beliefs when it comes to the "big" things in a relationship, and under my constraints, what you have with the father of your child comes no-where near to being a "partnership". So the point I think I am trying (very badly) to make, is that I think that you have been trying far too hard to be a caring and reasonable partner, when he hasn't been trying at all!
When I was young - and I got married to my first husband at a very young age - the books I had read, the films I had watched, the poetry we had to study at school, led to a very naive, and immature me wanting to be "in love" and to desperately wanting to be "loved". I am afraid @forfarhill that your thread here very much leads to me thinking that you also want and need the accomplished ideal of the 'romantic partnership', one that is so much more than the sharing of sex with our "significant others". I still have enough hope (and naivety?) that for the majority of relationships, that sort of relationship can/does (still?) exist.
But please realise OP that that is very sadly not what you have with the father of your baby, and by all that you have said, that isn't going to change under any of the current scenarios, so please, please, please OP, don't give him anymore chances. Even if he did "pass" this ultimatum, he will cannot change his inner character, as to do so would need an incredible amount of desire (from him) to succeed, and also the stamina, resolve and patience for such a change to take place, which could easily take several years, if it could happen at all. You are worth so much more than that OP, and if you still don't believe me, or anyone else about that, at least believe it for your very dear child. In your case, both you and your dear child will be much better off if he doesn't ever live with you again, and if you can help manage your child's expectations of him - without denigrating him - that would be even better.
Please believe me OP when I say that I know how difficult and scary it is to walk away from what might (but is highly unlikely to) be one's only chance of living in a traditional and happy real life partnership. If the romantic and loving partnership with another person doesn't happen - for whatever reason - I still truly believe that both your, and your wonderful child's lives, will be so much better long-term without your child's selfish father living with you. 🧡