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?

sorry guys but that was just a hypothetical situation. i'm not in that situation but it's a common one