He killed for you
You had everything you needed. Horses, a bit of cash in your pocket, and Billy by your side. You could both flee this godforsaken town and be free together. No ties, no bounties, and no disapproving fathers.
Ever since the first time Billy had seen you, he was smitten. A little over a year ago, your family had moved to New Mexico with your father's store business, hoping to find somewhere he could make a good profit. Billy had seen you outside the store, helping your parents load boxes inside and he couldn't help himself. He had to know your name.
One thing led to another, playful teasing turned into flirting, which turned into stolen kisses, and then before you knew it, you were sneaking the outlaw into your bed once your parents had gone to sleep.
All of this your father knew, well, besides that last part, and he hated Billy for it. Claimed he was a "no-good outlaw" and that he would only end up hurting you in the end. Every time, Billy reassured you with gentle kisses to your face that he'd never felt before what he felt with you. That you were all he needed.
You trusted Billy, you loved him. But you also had to come to terms that he had made some mistakes in his past. You'd only realized this the day you'd set to run away with him.
It was in the late and dark hours of the night. You were quickly packing your bags, strapping them to your horses, when a man, very clearly intoxicated, started hobbling over to the two of you. Billy saw and, without a thought, moved to stand in between you and the man, shielding you from potential danger.
And danger was what it was. After a few barked insults, the man pulled a revolver out of the back of his pants. Billy's instincts rose rapidly and the next thing you knew, he had pushed you to the ground, standing in front of you, pulled his own revolver and shot the man dead.
After a few moments of silence, you open your eyes to Billy helping you up and pulling you into his arms. He was saying something, most likely an apology or some reassurance, but all you could understand was that Billy had killed someone in front of your own eyes.
"Oh, babygirl, please don't look at me like that. I did it to protect you. I had to." He pleaded with you, putting his gun away with one hand, gently gripping your cheek with the other.