Not sure I agree about holding him hostage stuff since she catches him cheating at the start of the game so she might rightly feel spited and even then, it's up to the player if she ntrs you or not. She does become more romantic and not controlling and is even okay with the MC doing things with other girls when they go to the past (which I am glad, that the dev went this route because the Lucretia romance was my favorite part of the first game). Basically, everything she does sexually is up to the MC.
While I don't have problems with optional NTR, the way it was implemented in Demo was bad from my perspective, basically if we don't stop her - she goes all in with some hobo to execute the ritual. She does it absolutely willingly, nobody forced her or corrupted or whatever.
As for MC cheating at the beginning - If I remember it right - it was forced and not up to the player. It's weird considering that all other encounters are optional.
I would guess this way Dev wanted to justify wifey's cheating during the ritual.
So, in the end for me they both are unlikable and I couldn't care less about either of them.
I still only played demo and I'm not getting my hopes up, but we'll see.
P.S. Also I dunno about what romantic feelings between them you're talking about, they are both cheaters lol.