Yeah, it's a bit shady he is keeping so much from her. But he had observed when they were younger she was (and still kinda is) afraid of big men. He keeps his human form a secret partially to put her at ease and also in fear of her rejection of him. Though he said shinsu grow up all at once, I think that might apply only to their beast form, as he is clearly an adult in human form first and Bredee hasn't seen his human form in a long time.
If I was him and knew I would grow into a big strong man my partner would be fearful of, I would have taken every opportunity to be in human form so she could have gotten used to it. He could have kissed her by now.

Ok ok i get it... Amon likes her blah blah holding back blah blah....
But am I the only one that's kind of annoyed that she's in the dark about multiple things about him. I don't know if he's doing this to protect her but either way I just don't like how it's going right now and it's sort of pissing me off, is it just me or am I being too sensitive ( ̄へ ̄)