Actually, Ed seemed pretty fond of Nina, going as far to say that she should be his sister.
Her death pushes Ed into leaving the military, much to Roy's shock.
Ed's talk with Barry the Chopper:
And to be honest, I've been looking into your work, it's quite interesting. "Winry janks a chain to get his attention." Yeah, not right now, Winry. Y'see, just the other day, I saw some horrifying stuff. Naturally, I was disturbed, since it involved a friend of mine. But, I got to admit, it's opened my mind a bit. My life just seems to revolve around the grotesque, so I'm even drawn to it now.
'Heh, yeah, as a butcher, I can totally relate.'
And y'know, I look at you, taking beautiful subjects and turning them into incomprehensible clusterfucks that're impossible not to find amusing. You really inspire me. I think you inspire a lot of people. Sure, Society may look at you as some crazy freak, but not me. Not me.