Responses

I think the main reason they aren't couple yet is simply because the fl want to focus on her revenge and making thinks better first. If I am not wrong in chapter 79 or 80 she mentions that it's not time yet (for romance) cause she still need to deal with pope, get her property back, help the people of her descendants and other thing
Basically I said that Isaac isn't a bad ML. The problem is his omnipresence but lack of romantic progression. It's not like they have war to stop or anything so there's no real reason why those 2 aren't a thing yet with the amount of time they spend together.
I can compare it to another story named I only Treat Villains where MC and ML are constantly together and there's little romantic progression. But I that story, they have bigger problems and can't trust each other so of course they aren't in love. But we see them get comfortable with each other to the point where they start flirting.
But Isaac come regularly to reach Mel alchemy and you're telling Mel they aren't fcking yet? When is it then? When the Pope evades the capital??