When you don't care about what the person you love looks like, because looks don't matter. When you truly love someone, you're "blind" to their appearance.
-"Why are you in a relationship with that person? They're so ugly."
-"Because love is blind. It doesn't matter to me what they look like, I still love them."
The famous saying states that "love is blind". So if your girlfriend catches you cheating, she didn't love in the first place because she should have been from the fact that she loves you. In other words, if she loved you, she shouldn't have seen you cheat.
Person 1: "Bro my girl dumped me after catching me with Lisa"
Person 2: "Damn really? You know what, she didn't love you because love is blind."
Aw hey! That sounds like my thing! Boy am I glad that people are publicly talking about THAT instead of my thing! It's not like my thing is infinitely worse or anything.
Hym "Man, I don't even get free alcohol OR women trapped in a house with me! Those love is blind guys got it made. I don't know what they're complaining about."
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).