In episode 2.19, The Guru, Guru Pathik tells Aang that in order to control the avatar state at will, he needs to let go of all earthly attachments. Aang was hesitant, since that meant he’d have to give up his love for Katara.
But wait a minute… Avatar Roku had a wife, but he was able to enter the Avatar state at any time. Avatar Kuruk also had a lover, but they never mentioned any trouble with the avatar state.
Was Pathik just mistaken? Is it just something Aang has to do? Who knows.