I wanted to send you some s. Just the fact that you feel this way already shows that you are a caring and loving mom. Being a nurturing mom is about so much more than breastfeeding, and your LO won't be disadvantaged as long as you give him all the love and care he needs. My mom barely BF'd me (I was born early and stayed in the hospital for jaundice, so I got mostly formula from the start--it was the 70s...), but I don't feel disadvantaged. She's the most loving and generous person I know, we share the most amazing bond to this day, and I've grown up happy and super-healthy. Like, I never even got colds growing up. I'm not saying it's ideal, but we don't choose the cards we're dealt, do we?...
My two cents on this is... I think it's really, really important for you, for your LO and for the new baby that you have a supportive and stable home. You WILL need your husband's help and emotional support, especially with two pregnancies close together. Marriage means sacrificing and compromising, sometimes... or many times! Hiding something so big from your husband doesn't seem like a good idea, even if he never finds out--the "secret" will always be there. If I were you, I'd try one more time to talk and present objective arguments as to the safety of donor milk, and if he is not convinced I would respect that. You need peace of mind at this time, it's not worth adding more stress one way or the other.
Wish I could say something more helpful in practical terms... I know it's hard, mama! I'm here rooting for you.
PS. Can you still pump a little bit extra these days? If so, perhaps you could store some?