I was vehemently against rehoming until I adopted my dog at 8 months old, from a friend who couldn't cope with him. It was 100% the right decision for the dog, and for the owner. I take him to see his previous owner occasionally, and she always comments on how much happier he seems now, and how much his behaviour has improved. She says it brings her a lot of comfort, because he was plain unhappy living with her.
At the end of the day, life happens. You weren't expecting such a terrible pregnancy, and the reality is that you can't manage. Something has to give.
You need to properly sit down and talk with your partner. You need to explain that if HE wants to keep the dog, then the dog will be HIS dog, and he needs to walk him twice daily, take care of his mealtimes, all training, and 100% of the poop. Because you literally cannot. BUT you also need to think of what you are capable of doing. Maybe 5 mins of play with the dog a few times a day. Taking care of brushing him. Just something, if you are going to keep him. Bonding with him will help you as much as your dog.
You guys also need to consider if you can find a way to afford doggy daycare (ideally), or otherwise a dog walker.
You need to explain to your partner that if he's not willing to do these things, the dog will need to go to a home where he can be taken care of properly. This isn't fair on the dog. He's a living, thinking, feeling creature, and he sounds like he's going out of his poor mind.
I also don't like the sound of your partner. The whole point of partnership is teamwork. You're supposed to work together.