Ander didn't want to leave Jamie so soon, he wasn't even listening when Jamie had asked him to leave.
Ander is a Twenty-Four years old boy, who still has that mind of a fifteen. He has always been so considerate on people, he doesn't things the way he wants to and has a good sense in differentiating what's good or bad, which seemed like more reason why Rita had choosed Xavier over him. He was a softie at heart and had grew so fond of Jamie cause Alice was given birth to after one year before Ander was born. Jamie nursed him together with Alice just until he was six, then Rita felt like it was time for her go take her son back and that was how they got separated.