OP, while I fully accept this puppy is utterly adorable now, I'd like you to fast forward to say ten or eleven months in the future. Your pup will be at the "teenage" stage, your DH will be a distant memory, and you'll have a toddler plus another child. It's a cold wet night, the toddler's teething and you're trying to juggle all teh domestic responsibilities and walk the stroppy teenage dog whose recall has just gone out the window.
I'm involved in rescue, and there are a number of risk factors for dogs to be relinquished. Unfortunately, your scenario pretty much completes the "perfect storm" checklist:- puppy at the teenage stage, young child under 2 in the house, adults in the house not in agreement about buying the dog, marriage breakdown, breed which is high-energy. The only factor missing is the financial one - please think through how you might be able to afford this dog if DH leaves - think about insurance, vet bills, worming, grooming etc. You mentioned you don't drive, how will you get DDog to vet appointments, training, grooming etc.?
Any breeder with a shred of integrity or decency would have this pup back tonight - it will be easy to rehome at this stage. Unfortunately, as others have said, rescues regularly get a bulge of abandoned pups every spring, and there's another point when dogs become teenagers and are not so fun anymore and the cuteness wears off. Yes, your DS would be upset if the dog goes now, but not nearly as upset as he will be if the dog has to go in a year's time.
Please, please think through how you would be able to give this breed/type of dog the energy and attention it needs along with your young DC (can you really, honestly commit to at least two hours a day of exercise once it's fully grown and it's bones have developed?). If you are going to be a single parent, would owning the dog for the next 15 years impact on any plans to return to work? You can't leave a high energy young dog all day if you do, and do you have easy access to doggy daycare/kennels/dog walkers where you are? Can you afford this?
Dog ownership with young children can work very successfully, but it needs a lot of commitment plus time and money. You've been landed in a horrible position by your numpty DH - I'm really sorry about that. I'd just like to ask you to please, please think through the issues I've mentioned and there is nothing wrong with being honest and not wanting to deal with them. For the pup's sake, and it's long term welfare, returning to its breeder may be the best choice to make tonight.
If you do decide to keep it, I wish you every success, but I would strongly advise you do take up training classes - they will help enormously and have been proven to have a protective effect against dog relinquishment, especially with a high energy spaniel.
Once again, I'm sorry you've been put in this position, and it won't be an easy choice.