Despite that Teela can sometimes get annoyed by Adam's childish behaviour even before she had learn that he was He-Man this whole time but still cares for him and startring to have feelings for him.
The deal of her feelings was sealed when Teela said that you are my Hero in the original series she was attracted to He-man, and was annoyed by the foolish behavior of Adam.
The decision of Adam not to reveal his secret was no mistake it was a adult choice.