We had a thread on /lounge/ like this, and I think I pointed out even if you were happy with your beautiful Saya, she's still visible in her real form to the rest of the world. People would start wondering why people are going missing in the area, and if police knock on your door for information they'd be highly suspicious of the foul stench coming from your pus splattered house, nevermind the human remains in your fridge.

And let's say before you can be blamed, Saya kills them and you move. Someone is eventually going to see her, there would be an international hunt for this disgusting flesh demon and people will want to know why you're taking care of it. Constantly having to move and hide somewhere else is just too damn stressful!

Oh, and she's using your semen to make alien babies that will take over the world. She also dies in the process, so your love won't last long.