By doing that he is a worst uncle ever. Heck, even if she is his daughter too (just speculation), its fine since he is pretty much the last man in walled off town. Like, imagine if you were Ami, daaaaamn. You love the girl, you do everything for her, making her life a breeze, she knows that you love her and accepts your help as if it goes without saying, but she fks everyone behind your back and lie you in your face, giving hope. I would be livid and miserable, you have to be the last piece of shit to do that to a person who actually loves you.