Well, he actually called her mom through the entire first season. Believe me, I had a marathon today and it was bugging me. He kept referring to her as his mom and he called her mom to her face. That’s what he’s been raised calling her and I guess he’s just going to keep doing that.
I was a little upset that he suddenly cared about her, but I think that can be explained by her telling him she loved him in the last episode. I think he’s finally realized that she does love him.