Now may be a good time to set your first boundaries in regard to your mothering. Your H chose to leave his family. I'm sure he wants to maintain a bond with his S. But your responsibility is to your child and if you don't feel it's a good idea, it's your call. Especially for a nursing babe.
I don't see how it's a co-parenting issue. You can't just unplug the baby and expect him to be fine for H's sake. I'm sure it would be easier for H in many ways to have baby weaned, but is it best for baby?
If your son is still actively wanting to nurse, that means he's still getting something from the bond, either nourishment or emotionally.
You don't have to imply guilt or make it a power play. Just state that you thought about his request and don't feel it's in the best interests of your son right now. I think you're in canada? He can't take the child into another country without a notarized consent to travel from both parents anyways. Then put it aside and don't worry about that decision anymore. The stress isn't going to help you get through this time.
You're questioning your every move now because of the fragility of your marriage. But, imo, don't budge on your mothering standards.
My friend's H left right after her D was born and there was an outlined schedule for the first 6 years for visitation/co-parenting. No overnight visits until I think 2.5 years old. Look up online and see if you can find some other examples of parenting schedules for toddlers.
