 If you liked
Happy Sugar Life
|
 ...then you might like
Kimi ni Koisuru Satsujinki
|
Both stories tell the tale of a person, which kills for the sake of a relationship.
Not Happy Sugar Life, nor Killer in Love end on a happy note, which feels realistic to see them not getting away with their murders.
If you like to read a more bloody, more Gore heavy manga, I would recommend Killer in Love, as it shares some distinct similarities with the way that the protagonists handle critical situations (by murder lol).