This phrase arises because when people become lovers (meaning people who have engaged in sexual activities from deep kissing to full genital intercourse and everything in between) their bodies have a oxytocin bond. This sort of bond makes people able to overlook things that would be in other relationships rude, harmful or disgusting.
This is the same bond that makes parents love and talk goo goo lovey talk while cleaning baby poo out of every thing in a 10 yard radius of the poo-splosion.
Yes, lovers are blind, also deaf, mute and unable to smell.