He's made me move into a spare room on a blow up mattress even though I'm now heavily pregnant
WTactualF??!! You shouldn't be made to do anything you don't want to in your own home.
Go back to your bed and if he doesn't want to sleep with you, he can move into the spare room and sleep on the blow-up on the floor... twunt!!
If he kicks off don't hesitate to call the police and have him removed from your home. A night in the cells or dossing on a mate's sofa might give him the wake up call he needs.
If he didn't want another dc he should have tied a knot in it. The fact that he's using his failure to have a vasectomy or control his sexual urges to turn the dc against you is beyond despicable and indicates that he's not fit to be a father to one, let alone three, dc.
This situation isn't going to resolve itself anytime soon and is likely to get worse after the arrival of your new baby boy who, sadly, is likely to feel the wrath of his df's tongue at an early age.
For this reason I suggest you consult a solicitor who specialises in divorce & family law with a view to ascertaining your legal entitlements, and make it clear to your h in no uncertain terms that any more of his nonsense will result in you petitioning for divorce on the grounds of his thoroughly unreasonable behaviour.
You don't deserve the treatment he's meting out to you and I sincerely hope you won't feel obliged to suffer it 'for the sake of the dc'.