It must be hard to have to be fought against doing something so natural... I'm sorry this is going on in your life right now when what you really need is lots of support.
The only advice I can think of is...
1. Could you print out a bunch of reasons why breastfeeding is so god for you and your son and give it to your SO? Is he receptive to that sort of thing?
2. Maybe schedule an appointment with a lactation consultant that you and your SO could go to together and have someone else explain to you and him the benefits? Would he go for that?
3. Maybe if nothing else works he would consider you pumping and giving your son BM in bottles? That way at the very least he is getting the BM?
I hope you work something out either way you go!