is it wrong to leave someone

so this question has been in my head lately. is it wrong to leave someone for someone better? let's say a man leaves his woman of 5 years or something because he fell in love with someone more interesting/beautiful/funny/smart.

from what i've seen and read people tend to consider that asshole-ish. but at the same time people also espouse the greatness of true love..  is breaking up an established relationship justified in the the name of love?