I find Separate Peace relatable because of its setting minus the early years of World War II. And because of the themes surrounding the novel - competition; though you might find it confusing who the main character is really competing against. "Beginning with a tiny incident among ordinary boys, it ends by being as deep and as big as evil itself." The title will sound ironic by the end of the novel because even this "separate peace" which the two best friends created will eventually be distorted. The inner war in this book is more poignant than WWII itself.
“So the more things remained the same, the more they changed after all. Nothing endures. Not love, not a tree, not even a death by violence.” Since nothing endures, we have this need to relish each fleeting moment. And that's how you will mostly feel about one of the characters.
Speaking of fleeting moments, The Fault in Our Stars is about two characters who cherished each other's company knowing that one of them will eventually die sooner that most of us are expecting. It's probably the "perks of cancer" or "side effects of dying."
That quote reminded me of an interview we did with the late painter, Joey Velasco. We asked him which year in his life did he wanted to last twice as long. He said that the length doesn't matter, but the quality of life we live in those 365 days. It's how we create and treat those infinities in our given set of time frame.