Coming to add more to my comment:
I don't necessarily hate the concept. I don't even hate the "happy" ending. I just wish it talked more about the issues with fated pairs when you have your heart set on someone else.
In most omegaverse stories, fated pairs turn out alright because the two happened to not be connected to anyone else and the inner turmoil is just between the 2. But here we have 2 couples who were torn by that fate.
It's easily missed, but it briefly mentioned that the fated pair omega (I'll refer to him as FPO) locked himself away whenever he was in heat and the drug overdose is what put him in a coma. That's not Nanase's fault, but certainly Nanase didn't try too hard to help.
Rather than Nanase and FPO work something out, both of them go through extremes. Now, I'll talk about how I wish Nanase's route went:
Nanase seems straight forward in his pursuit of Eito, but suddenly his personality changes and he seems self-sacrificing. Wurt?? The author seems to miss the ingredient I was looking for. Is he insane, but sweet for Eito? Or was he sweet but driven insane by circumstances? It starts out as one and then the author remembers they wanted to do the other. Honestly, I prefer the former but would like the latter play out. For that to happen, a disappearing act shouldn't have happened. I wish he was confronted with his distorted feelings of not liking the fated pair system. It's weird we're shown his distaste for omegas, but he's desperately trying to change Eito into the thing he hates rather than him not being with him as he is. In that case, he doesn't hate omegas, he just doesn't like being controlled by their pheromones.
I wish FPO didn't have as much screen time as he did because it added no value.
They didn't bother fleshing the characters out so most of the scenario is a cop-out.