Norwegian Wood by Haruki Murakami
I think Toru might also commit suicide not long after the end of the book, just like his old friends Kizuki and Naoko, due to being lost in the search for identity.
The first one to commit suicide in the trio was Kizuki, who took his own life early in the book, and his death was sudden. It wasn't until I reached the later part of the book that I began to understand that his suicide might have been due to a lack of self-confidence, leading to being lost in the search for identity. We learn from the memories of Naoko and Toru as they grew up that Kizuki would often complain about his flaws when alone with Naoko and would frequently become frustrated because he couldn't hide his weaknesses. Toru mentioned that he usually didn't notice any significant emotional fluctuations in Kizuki, but Naoko explained that he only dropped his guard when he was alone with her, often getting emotional because of his dissatisfaction with his own weaknesses. Naoko then said that Kizuki didn't know that she actually loved both his weaknesses and strengths simply because she loved Kizuki. It's a simple truth: she loved the entirety of Kizuki, flaws and all. Without these flaws, he wouldn't be Kizuki, and Naoko wouldn't love a flawless Kizuki. Kizuki was always trying to become a more perfect version of himself, but people can't be perfect; each of us has our own unique flaws.
Unfortunately, Naoko fell into the same predicament. When Naoko was recovering her mental state in the sanatorium, she had already moved on from Kizuki's tragedy and fallen in love with Toru. However, her idea was to first fix her own mental issues, become a self-sufficient, independent, normal person, and then move out of the sanatorium to live with Toru. She didn't want to be a burden of Toru. Naoko herself didn't realize the simple truth that every person has flaws. She believed that Toru wouldn't accept and accommodate a flawed her, just as Kizuki believed that Naoko wouldn't accept and accommodate an imperfect him. However, it was this desire to become better that worsened her condition and led to the same tragedy that happened to Kizuki happening to Naoko again.
Naoko's death was also related to Toru not taking Naoko out of the sanatorium and living with her in time. During Naoko's time in the sanatorium, Toru found himself in an emotional whirlpool: he didn't know how to choose between Naoko and Midori.
Throughout Naoko's time in the sanatorium, Toru constantly questioned his ability to take care of Naoko if he were to have her released from the sanatorium and live with her. After Naoko's suicide, he became even more uncertain about his ability to love others. At the end of the book, after deciding to be with Midori, he lost himself in a phone booth in the rain. My guess is that he lost himself because he was unsure if he could give love to Midori and make her happy. Naoko's tragedy had completely plunged him into self-doubt. This is why I think Toru might also follow the path of Kizuki and Naoko in committing suicide.
We can strive to improve ourselves positively, but we don't need to pursue perfection; no one is perfect. We are all unique individuals who can be replaced by no one. This shows the importance of love. Love is inclusive, and love can bring imperfect people together, heading towards the happiness. This is a truth that non of Kizuki, Naoko, and Toru understand. The trio was like three people drowning at the same time, each holding onto each other's fate, entwined with each other, sinking into the tragic abyss.
"'To tell you the truth, though,'Naoko went on, 'I loved his weak side, too. I loved it as much as I loved his good side. There was absolutely nothing mean or underhand about him. He was weak: that's all. I tried to tell him that, but he wouldn't believe me. He'd always tell me it was because we had been together since we were three. I knew him too well, he'd say: I couldn't tell the difference between his strong points and his flaws, they were all the same to me. He couldn't change my mind about him, though. I went on loving him just the same, and I could never be interested in anyone else.' Naoko looked at me with a sad smile.
-- p154, Norwegian Wood