Sister-in-law maybe interested in blondie or not. But brother-in-law is hooked. That's a very strong first impression. It looks like they are a fated thing. So...
The bad omen must not have been about them being together. I could be wrong but I doubt the author will take the dark path and make their fates death. That's the only logical result if the omen was about them. I doubt they'll end with other people either since that would be too bitter of an ending given the tone so far.
It must be about the environment/conditions they got together in. Their bad ending happens eight years in the future. That leaves Han-Eol and Da-ae eight years to change things to make the conditions different. Along the way they are given the chance to get together themselves. My guess is everyone will have a happy ending.
Stalker-san has been hyped up a lot so he is either what has to change or is a huge ruse which will get resolved soon. It's fairly certain who he is by now. The rest of the arcs are probably going to be Han-Eol and Da-ae making the changes (they may or may not figure it out ahead of time), adapting to the results of the changes, finding out that they can be together permanently (their resolution), and the in-laws getting together under the right conditions (the in-law resolution)... all that happening in any order.
EDIT: This leaves an interesting question. Earlier Da-ae asked why eight years and that opened the possibility that it was the stalker who initiated the time loop. They just got caught up in it. If that's true then the omen was predicting everything happening in the present (including events after the time loop). So, how much of this is up to fate?
In the first chapter Da-ae's mom said the psychic told her "when those two are close to each other, dangerous situations occur." Even if the in-laws don't get married they will be "close to each other" because of Han-Eol and Da-ae's relationship (at least as far as a stalker's perspective goes). They will be pulled together because of family. That implies what Han-Eol did by saying they're dating put everyone in danger. If the stalker is the person who initiated the time loop then either he has to win by keeping sister-in-law away from her family or they have to win by defeating the stalker. That's what has to happen if "fate" is to be taken seriously.