It's perfectly reasonable for him to be honest about not wanting to live with a large dog,
It's really good he is sensible to be realistic about his ability to cope with that, we have thousands and thousands of dogs who owners, and breeders, didn't care if they could meet a dog's needs,
You are the one that will be with it most of the day, and looking after it, but if that makes the home a place where part of the family does not feel comfortable, it is going to cause problems,
It a commitment to an animal that will last over a decade, if someone has even a single doubt, then to push it on them, is not just unfair on them, but hugely unfair on the dog, who always ends up paying the price of that decision.
Is it a deal breaker for you? Living without a dog, only you can decide what you want more, a dog or this man.
You will run into massive problems very quickly if he isn't totally on board, If he choses not to become totally familiar with K9 behaviour, and training techniques, you have to really apply yourself to be successful, and genuinely interested in the subject,
Unless a dog is trained with consistence from all family members, it will never reach it's full potential, and the dog has a limited life.
If you want him to want to do it, he would have to fall head over in heels in love with dogs and the breed,
take him to an agility demonstration, but it does tend to be an acquired taste, you are most probably flogging a dead horse,
If it's not for him , it's not for him, it's not fair on a dog to live with someone who doesn't like dogs, so if he is only going along with the dog thing for your sake, do the dog a favour and don't get one.