Plus it's such a raw and vulnerable thought, and if you're with someone you trust or love so much, you feel more of the need to tell them because honestly, you're scared of what you might do to yourself. If there wasn't really any suicidal behaviors before someone tells you they're going to kill themselves because they're without you, it has a good chance it's manipulation. Though, this guy is like NOT in the right state of mind. You see he is embarrassed because he probably knows that isn't something he wanted to tell Nanjo. We never really saw him try to tell Nanjo about his self destruction either. I really hope he gets the help and recovery he needs in the story, even if the ending doesn't include the 2 being together

As someone that’s been on nanjos side and hearing someone you were in a relationship say they are going to kill themselves. It’s definitely not something you should say to the other person in an attempt to win them back if anything it pushes them away even more.