Ahh, so great to see this completed, I'd only seen the first chapter a few years back.
Regarding the "tragedy" tag and the ending:
Both couples (Naruko x Manuel, Patrick x Osmond) make it out alive so I'd count it as a good ending. Naruko can just chase off the demons around Manuel in the future.
9/10 for compelling story and great art. Only wish that it'd been longer, even a short epilogue showing more of their lives after the events in chapter 6.