I have a suggestion for a compromise, since you said it is important to you to be in your new sister's life. Maybe you could approach your dad and say that you do respect his wishes while you are in his home, but that you won't feed your son in the bathroom bc that's not sanitary and is insulting. You could then ask him if it would be OK to feed him in another room, such as another living room or a bedroom.
I'm not excusing his behavior in the slightest. I think we all agree that he was being ignorant and rude and you were absolutely right (and brave) to stand up to him. I was just trying to think of a way that you can continue to be in his life and also continue to nurse your son with dignity.
I think it's important for others to respect my wishes when they are in my home. If I want to BF in my living room, I will do so without apology bc it is my home and in my home we follow my rules. I don't wear shoes in my home and I expect others to respect that too, even if they don't like taking off their shoes and don't do that in their homes. But if I am in someone else's house and it makes them uncomfortable to see me BF in front of them, even if those attitudes are coming from ignorance, I feel I must respect their wishes bc it is someone else's home. In my parents' house I nursed in the sun room while everyone else watched TV in the living room. Not bad in the slightest--it was lovely!
I hope this came across in the way I intended it.
