Leon was having a hard time dealing with los ganados until you showed up to help him.

A guy with a chainsaw cut your hand off causing it to fall into a lake along with your gun, Leon quickly ran to you in dismay until he heard you say, "Damnit... My favorite gun!"

He looked at you with shock and confusion at how you had a severed hand and all you cared about was your gun. "Is that what you are worried about?!"

Maybe it would be good to tell him about your past as an Umbrella experiment.