War stories are frequently tragic but rarely involve less than a squad and both your examples focus on two people. If the number two isn't that important I would suggest:
The 13th Valley
by John M. Del Vecchio
Matterhorn: A Novel of the Vietnam War
by Karl Marlantes
The New Leaf Book Club selection for September could be considered tragedy and involves friends beginning as young children until early twenties I think.
Never Let Me Go
by Kazuo Ishiguro
As far as tragedies involving two people, all I can think of is a couple farther and son stories that I liked very much.
Wintering
by Peter Geye
Medicine Walk
by Richard Wagamese
Now that I think of it, Medicine Walk has a story within the story of the father's buddy bond with a friend that begins in late adolescence in a north woods lumber camp and involves tragedy.
One other that, with a big enough hammer, might fit, sort of, is:
Thirteen Moons
by Charles Frazier
The primary tragedy here is the 1830 Indian Removal Act's impact on the Cherokees from Appalachian North Carolina. Much of the story takes place prior to 1830 as white people begin moving into the area. The buddy aspect is between a white man and a Cherokee man. Reading a few reviews, I see people referring to that as father/son but I'm recalling it as more of an equal but different relationship. It's only a small portion of the book but, well, it's by Charles Frazier who I rank up there with Steinbeck.