Why do you think Gene did nothing as most of the other boys made plans for military service?

In my opinion, Gene is far more worried about Finny at this point than he is the war. Gene is carrying around a lot of guilt, and Finny needs quite a bit of assistance. Gene will be there for him.... the easy thing to do would be to leave.... forget it all. None-the-less, that would simply be trading one war for another.