Matt said, "I promise to clean within the hour."
Liar.
Mello said, "I promise I won't leave the wrappers on the floor."
Liar.
Matt said, "I promise to keep you safe."
He tried, but he's still a liar.
Mello said, "I promise to protect you."
He tried, but he's still a liar.
Matt said, "I promise to make you stay,"
Truth.
"... and live till you grow old and die."
Well, never mind.
Mello said, "I promise that you won't die because of me,"
Liar.
"...and you'll love someone without me."
Still a liar.
Mello always tried to keep his promises. In fact, he would use guns to make sure that they would. His glare might ensure it and his bad posture and intimidating self might keep away anyone that could hurt him... but maybe not idiots?
Matt made sure his promises were kept and remembered them through everything because if he didn't keep them, the promises wouldn't just break, so would he. Depending on who the promise was for, they would probably hurt him anyway.
Mello knew how to pretend, to play the game of Life, to fight, but not how to tell the truth. That was his whole dilemma and he completely blamed the people who broke his trust, because he had a complete right to. ["Bastards ruined me."]
Matt was better at the game we all played than anybody ever could be. He played it as best as possible, just to make sure the ones he cared about were safe. 'Cause if they weren't... there'd be hell to play for those who took their safety. ["Nobody and I fucking swear it."]
Their promises were sometimes fun, playful, or just plain jokes both understood. ["Unless one of us played our cards wrong."] Others were different and came up with different circumstances. They weighed them down to the point of literal fatigue and depression, but...
...why lie?
Matt promised what he knew he could.
Mello tried his best to do the same.
They both became horrible liars.
Really, though, nobody ever wins the game of Life and love was never someone's prize.