Ginger ..... again, I'm so sorry that's his attitude and well done you for not putting up with any of his selfish stupid shit. Yes, stupid, because if he'd treated you with a bit of respect and as an equal adult he might just have found that between the pair of you, some sort of compromise could have been thrashed out to everyone's advantage. I can't believe the way he spoke to you - quite obviously he sees you as a housekeeper and nanny and nothing else, and an unpaid one at that (though it's not surprising seeing as he was quite happy before to scapegoat you rather than pull his daughter up - for her own good FFS - over potentially damaging accusations). Please please stick to your guns about him moving out - anyone capable of speaking to their partner like that won't change even if he does try to soft soap you now with his insulting "don't be silly" .... I'm sure I don't need to tell you that he'll want to stay because it's easier for him if you remain the little obedient "wifey" doing all his childcare.
I really admire you, as (most) others have already said for protecting yourself and your children from a situation which could very likely be very disruptive and stressful. Clearly, this "choice" of his would never work in a million years when he doesn't value your opinion or feelings one iota and would almost certainly undermine you at every opportunity. Anyone doing the vast majority of day to day care for a teen who knows she can get away with murder will be on a hiding to nothing and your life would be an utter misery.
As for you Daisy what is it with you ? .... are you reading a different thread to the rest of us ? Of course you're not but hey, don't let the facts of the matter as described by the woman actually going through this situation spoil your goady fun. Are you incapable of imagining for one second how the OP must feel right now ? ... she's pregnant, and is having to face up to the fact that her so-called partner sees her as nothing and nobody, seemingly existing only to do his bidding when he demands - no discussion, no respect. Do you get off on being so disdainful and insulting ? ..... how bloody rude you are to refer to the OP as "a girlfriend" when she's 6 months pregnant and up until a couple of days ago had presumably been looking forward to a long term future with this man .... the same man who's now revealed his true colours (though admittedly he's not covered himself in glory before) as a very selfish user with what amounts to an extremely sexist view of women by expecting Ginger to fully accept another - and troubled (as indicated by serious lying) child - with a single murmur of dissent. I think she's very brave to stand up for herself given she's 6 months pregnant - a lot of women would perhaps put up with being treated so badly due to the new baby's soon arrival. However, make no mistake and obviously Ginger knows this - life as a single mum and especially with a newborn won't be easy and I'm sure she's hardly jumping for joy over all this ..... so how about you lay off with your holier-than-thou nastiness ?
Perhaps Daisy you are the OP's DP in disguise or even the SD ?? ..... or maybe you're a so-called "surrendered wife" ?! Can't understand your mindset otherwise. "Sounds like he'll be better off" ...... oh per-lease .... this poor little put upon man who, remember, does NOTHING for the OP's children but expects OP to do EVERYTHING for his because he tells her to (and not because he courteously and respectfully seeks her agreement). And yes, it's always very sad, when, for whatever reason a child doesn't live with both its parents in a happy household but this situation is NOT of Ginger's doing - you talk about "lack of compromise" as if the OP is being completely unreasonable yet when she attempted to speak to her partner about how this would work it was him who told her that a) her opinion doesn't matter, b) it's nothing to do with her and c) SD living there is his choice ONLY. Fucking hell - THAT is the perfect example of a lack of compromise and if you can't see that you must be on another planet - or, to use a well worn MN phrase, perhaps you're on glue !
The fact the new baby will be brought up without its father involved in its life on a daily basis is its selfish, arrogant, contemptuous father's fault so don't you dare try to make the OP feel worse than she already does by blaming her for this very sad situation - which could potentially have been avoided if her DP was any sort of real man who saw her as an equal worthy of discussion.
Ginger - keep your chin up sweetheart (I know that's a bit gushy). You're doing the right thing and setting a great example to your kids about how women should be treated by their partners (and the other way round of course).