This is typical 6 year old behavior, jshowers, and biomoms tend to be okay with it because they love the kids but stepparents tend to be more irritated by typical child behavior.
From your profile, it appears you're 23 years old and probably don't have any experience with children.
Just fake that you love him. Fake it, and the feelings will follow.
6 years old isnt too old and he i probably just a curious little boy and tends to forget that he has asked the same question over and over again