Oh sweetheart, if you were my daughter I'd welcome you home and you could stay as long as you needed to! I hope your parents can give some support, can you tell them the truth?
As much as you feel you lack strength for a big traumatic change now (and I really feel for you, sending virtual hugs), it will only get harder and harder the longer you stay because whatever is left of your self esteem will continue to be hacked away.
What you did with the rabbit was an act of love. You anticipated his pain of dealing with it, and acted to protect him from that, not only that, but you treated the rabbit with respect and care. You were motivated by a desire to support him at losing his pet. That was such a gently loving selfless thing to do- well done on your humanity and caring heart - your baby is going to be so lucky to have such a wonderful person for a mum.
When your baby arrives, leaving him will get more complicated, because any bond they create will complicate the decision.
Because he is a nasty person who is not interested in treating you with respect, but is interested in keeping you crushed and taking out any bad feelings he has on you, he will weaponise the baby to make you doubt your choices, feel like a shit mum, and also to l as another means to hurt you. For him this baby will add to his knife collection of things he can stab your heart with...
Instinctively he knows that you leaving is easier now than when baby arrives, you can expect him to become more nasty once you are vulnerable as a new mum because that is a time in your life when you need support and have a tiny wee life to think about, it is a really bad time to be in the company of and abusive person.
There are many uncertainties as you find your feet with baby, someone's they cry a lot and you don't always know why straight away, everyone figures it all out eventually (don't worry), but f* me you don't want someone pouring poison in your ear, blaming you, demanding you sort it out or accusing you if not knowing what you're doing and being a crap mum (which lets face it, is his likely approach).
Becoming a mum can be a big challenge, it's well worth it and wonderful too, but also tiring and with the willingness he showed to misread your actions and lash out with cruelty your new motherhood will be so so much harder.
Not everyone falls in love with their baby immediately, and that's ok, but many do and the beauty of that experience, however it happens, will be stolen and trampled if you are with him then.
Your strength has been undermined and stolen by this, which is understandable - anyone would in the face of such hateful acts... But it won't get any better and you don't want a lifetime of this for you or your beautiful child... reach out to any real life support you have and escape before baby arrives.