The original question had to be edited down. I think that Paul's affection for his comrades is reflective of how isolating the war experience was. The reality that awaits Paul and those of his generation is one in which the brutality of war overrides bonds to country, ideology, and general purpose of being. The only transcendental reality that awaits all of those who fight in World War I is slaughter. In order to offset this fairly brutal condition, bonds of friendship are formed. It is here where Paul's fondness for his colleagues is evident.
As the narrative increases, Paul is able to see their own tragic condition. Their states of being pathetic and sad victims of a war that was not their own doing become evident to Paul. In understanding this, Paul begins to understand his own plight. It is for this reason that Paul and the other "veterans" take the younger soldiers under their wings and nurture them in the latter half of Chapter 6.
While it does not offset the reality of death, Paul recognizes that the bonds between soldiers is the only condition that can be generated which might alleviate the sad condition of death that seemingly awaits them all. When Paul recognizes that he is "all alone," he sees a reality that seems to promise that death is inevitable for him.
In another sense, Paul's fondness for his comrades reflects Remarque's fundamental motivation. Remarque writes that his work is a testament to a "lost generation." The "patriotic enthusiasm" of the older generation was one in which young people faced death.
For Paul, bonding with his comrades and remaining fond of them is his only act of resistance. It is resistance against a war in which the young paid the price disproportionately more than anyone else. In this, Paul's affection for his comrades is an emotional response and a form of resistance to the forces that have condemned him and his colleagues in a war theater of death; in reality, not everyone died, but all saw that death awaited.