Shaw explains love and war by juxtaposing authentic love and realistic responses to war against false romance and false heroism.

In this play, Sergius represents both false romance and false heroism. Bluntschi, on the other hand, sees life realistically and represents genuine love and a pragmatic, rather than a heroic, approach to warfare.

Sergius pretends to be in love with Raina, the woman from his own class he is expected to love and marry. However, his true interest is in her maid, with whom he carries on a clandestine romance when Raina is not around. Sergius is also considered a military hero after winning a battle, but as Bluntschi points out, Sergius only won the battle because the other side was even more grossly incompetent than he was.

Bluntschi, in contrast to Sergius, doesn't pretend to be what he is not, and doesn't feel he has to play a cardboard heroic or romantic role. He deserts the battleground to save himself, which Shaw presents as a reasonable and positive response to his situation. He openly prefers chocolate to bullets. There is no false posturing in him. When he falls in love with Raina, it is based on genuine affection for her.

Shaw's play illustrates that is better to act in response to what our own hearts and minds tell us than to try to enact a false script of how life should be.

I tend to think that Shaw's treatment of war and love is to remove the romanticism that is so strongly attached to both concept.  Shaw was realistic enough to understand that society held cliched standards that sought to define both experiences to such a point that individuals had to second guess their own emotive narratives in both to ensure they were conforming to an external standard rooted in phony romanticism.  The romantic view of war made it out to be an experience of unquestioned glory and valor.  The fact that Bluntschii carries chocolates with him instead of bullets is an honest symbol of the fear intrinsic to war.  There is little Romanticism in a war, which is exposed as a "sham" in the work.  In much the same way, I think that Shaw treats love as an entity in which there is much romanticism and a concern about what love should be as opposed to what it is.  The hollowness between Raina and Sergius is representative of this.  Their union is one in which both are constantly plagued with expressing what should be said by lovers separated by war, even though it is evident that there is a hollowness to their words that both truly "get."  In this, there is a strong statement about what has happened to love and war in terms of social expectations controlling individual experience and feeling.  It is this treatment that Shaw seeks to address in the drama.