"The Things They Carried" is the first short story in O'Brien's collection of the same name and explores the topic of love with brutal honesty. It's best exemplified by Lieutenant Jimmy Cross and his love for Martha, the young woman whose photos and letters he carries with him.
Jimmy and Martha were in a relationship back in the States and basically still are when the story begins, but the reader quickly comes to realize that it is extremely one-sided and always has been. It's an interesting contrast to how wartime romances are described in less candid war novels. They often succumb to the temptation to portray love as the lifeline for soldiers, but O'Brien does no such thing. Instead, he shows how artificial that kind of thing can be, especially since Jimmy Cross starts off having the same kind of glorified conception of love and Martha.
From the way Jimmy Cross thinks about Martha and the way he describes her, it's soon clear to the reader—and eventually to Jimmy himself—that there are in fact two Marthas: the one Cross wants to be real and the actual woman. The former is the idealized version, who in all likelihood never truly existed. Cross puts Martha on a pedestal because that's what he needs. That Martha represents the pure image of the woman he loves and the future he envisions for them. The real Martha is not quite the same. Her letters are described as more friendly and polite than full of yearning. From the shadows of Cross's maniac love for her appears the truth that the whole relationship might mainly exist in his head. It's not that it never existed, but it was always more serious on his part. That realization hurts Jimmy Cross deeply.
There are other glimpses of love in the book as well, like the soldier who wears his girlfriend's stockings around his neck for protection and good luck. They all seem to support the main example of Jimmy Cross and Martha; however, war tends to corrupt love. It's nearly impossible to maintain its purity, as war is the antithesis of love and twists it quickly into something different. Jimmy Cross thought he truly loved Martha. That was probably true, at least in the beginning, but as time went by, up to the moment when he started to carry the pebble she sent him in his mouth, it had become something more akin to obsession.
O'Brien shows that while it's not impossible for love to escape war unscathed, that's not always the case. Just like men get wounded and carry on with the scars, love ultimately gets enlisted and weaponized as well.