How did you know it's him and not the bodyguard dude?
Well, i can Imagine satoko saying something like “live” or “even if my time is up you still have a future ahead” and considering shinpei stopped killing for a while just because satoko said so, he’s also capable of doing that for her sake. i know she cares about the bodyguard guy but I don’t think she’d write him something when she has shinpei and maybe she left the letters as a goodbye or to give him strength to get by when she’s gone. The old guy at chapter 1 talks as if he’s still longing for someone who’s long gone, waiting patiently. I think we know only shinpei is crazy enough to do that, a normal person would’ve just moved on honestly.
Also, he says he got married to someone he fell in love with when hes been told not to, so I think it’s obvious
I don't think that "a normal person would have moved on" statement is true. I know a bunch of people who never moved on after their spouse passed. They continued their life of course but their spouse was the one and they never had another.
Y’all i know we got like no hope for happy ending atp but double suicide is not happening. (As much as I wouldve preferred that) it’s shinpei reading her letters at chapter 1 I’m pretty sure. So he survives