How People Treat You Is Their Karma

​​​​​​Someone (A forgotten friend I ran into) said something that brought me back to reality. I was defenceless and really touched by his statement.
He said: "Sadeeq, if I have forgotten you, don't forget me."

There was this guilty sensation that enveloped me. This is someone that care less about me, he had forgotten me, and I reciprocated. I had reasons to pay him back in his own coin, but that didn't change the fact that I was wrong/guilty. 
I realized that two wrongs don't make a right. We shouldn't treat people based on how they treat us. We shouldn't allow people's negative treatment/attitude towards us to change us negatively. In that moment of reflection, I stumbled on this quote:

"How people treat you is their Karma, how you react is yours.