This one might just take the cake as the worst ending to a pornhwa ever.
I'm going to summarize it for those of you who are interested. Spoilers incoming, obviously.
The protagonist is helping out his boss/friend by keeping quiet about his many affairs (he's a lawyer who sleeps with basically all of his clients) in exchange for getting a nice apartment and whatnot. The friend's wife, who is actually the one with all the money, finds out about the cheating anyway, and when the boss/friend realizes that he's going to end up with nothing in the divorce, he decides that everything is the protagonist's fault and wants revenge.
As all of this is going on, a childhood friend of the protagonist comes back into his life after several years. The protagonist likes the girl, she's aware of his feelings, likes him back and they end up sleeping with each other. At this point, you start getting the feeling that they're going to end up together.
A while later, some thugs go after the girl to settle a debt and tries to sexually assault her inside a car.
She gets away and goes back to work right afterwards, where her boss is mad at her for suddenly leaving and then tries to rape her. The protagonist's boss/friend interrupts it but then immediately goes on to blackmail the girl by saying that he'll get rid of the thugs pursuing her if she sleeps with him.
The protagonist was already setting up a lawsuit against the thugs to save the childhood friend, but despite knowing this, she decides to agree to the boss/friend's terms anyway.
After that, the protagonist gets called to the office by his boss/friend, only to find him in the middle of having sex with the childhood friend. The childhood friend notices the protagonist but just tells the boss/friend to fuck her harder, suddenly not caring at all about the protagonist.
The manhwa then ends with a shot of the childhood friend looking at the sunset, thinking "This is the first time the sunset's looking this beautiful. I'm sure it's because I'm free now."
That is literally the ending. The boss/friend who was a scumbag throughout the entire series ends up winning with no repercussions whatsoever to his actions other than being forced to leave his wife.
We don't learn anything about what happens after that whole shitshow, but it's safe to assume that the relationship between the protagonist and the childhood friend crumbles completely, with them not ending up as lovers and most likely not being able to go back to being friends again either.
I think this is the first time I've given a rating of 1 on this website, but even that is a bit too generous considering what a trainwreck this was.