beta
The seme is not emotionally stable enough to be in a relationship and is abusing the uke by attempting to control him and literally strangling the uke to death to keep him from leaving.
The uke basically groomed the seme and only started dating him to make himself feel better. He's not in the wrong for killing the seme seeing as it was in self-defense, but he wouldn't have had to defend himself if he hadn't taken advantage of the seme's vulnerable emotional state.
These two are going to end up killing each other again unless the seme can get help and they both realize that they aren't good for each other.
A sensible ending for them will either be a bittersweet (but healthy) separation or a bloody tragedy.