I've never actually read the manga, only the fanfic of another manga it inspired. The author couldn't remember the name of the manga but here's what they had to say about it.
"It had a group of teenagers who planned a suicide pact online, became friends, got distracted by alcohol and general shenanigans, and ended up not going through with the suicide anymore... main female lead was out with one of the guys and she was thinking 'maybe in different circumstances, we would have been out on a date instead of out planning to die'."
I took out some stuff where the ellipsis are, since it was a side comment. They did mention the ending was kind of tragic though. I'd be really grateful if someone knows of it. Thanks in advance!