Okay, I’ll say what no one else wants to say. I think David got Nelson as a gift for Gillian and the kids. Knowing she wanted a dog, he probably visited the shelter and fell in love with Nelson, so he thought of Gillian and her kids. Nelson appeared during filming so I think David was the dog-gifter to Gillian. There’s no reason NOT to think that or assume that. :) I know that isn’t a popular opinion but it’s what I think, fwiw.