I think Rick is a recovering nihilist. Since he can travel between infinite dimensions, he sees all life, even his own, as cheap. Nihilism isn't enough for him emotionally, but every time tries to crawl out of that hole, his mind yanks him back because deep down, he knows, with a capital K, that there isn't a higher order to the universe. The tension between the arrogant asshole, and the broken philosopher is one of the things that make Rick an interesting character. That, and the fact that Rick is hilarious.