When James Potter bullies Severus Snape during a break from testing in their fifth year, Lily Evans finds herself caught in the middle of a love triangle. Her irritation at her childhood friend Severus for calling her a ‘Mudblood’ mixed with her frustration at James’ arrogance drives her to storm off in rage. James is beside himself for angering his crush so he begs his best friend Sirius to change into his animagus form to sniff Lily out and convince her to meet up with him so he can properly apologize. Sirius, wanting to help out his best mate, seeks out Lily and finds her alone, crying on a window bench in a study room. He teases her at first, until he realizes she really needs comfort. His arm slides up and around her shoulders and their eyes meet. Suddenly, they kiss, in a moment of unbridled passion. Lily is consumed by her overwhelming feelings, which encourages Sirius to feel up her skirt and grab her bum. He pulls her up and she straddles him, his head between her breasts, then Sirius flips her over and enters her, thrusting and climaxing quickly. As abruptly as it begins, it is over.
Immediately embarrassed after having sex with his best mate’s crush, Sirius quickly pulls up his trousers and cooly sways a step back from her, diving into an explanation as to why he’s actually there - for James’ sake - and proceeds to convince Lily he has no honest romantic feelings for her. They agree to never speak of the engagement ever again.
“Hey, so… uh.. I hope we can agree to not say anything to anyone about this. I kinda have a reputation to keep.” And I’d possibly lose my best friend, he thought.
Lily felt like she was stabbed through the chest. She didn’t know how to respond to this, so she probed, “Well, are you going to say anything to me about what just happened?”
Sirius leaned back, sat against the edge of the desk and shrugged, “What’s there to say?”
“Well.. then, what will you tell James?” Lily continued to dig for an answer that would reinforce her feelings for the recent intimacy.
Sirius paused and looked out the window behind her for a moment, thinking. “That when I found you, you were still upset and would have to think about it.”
Simple answer. His response left the truth intact but details omitted, so James wouldn’t know and Sirius was completely open to do whatever he wanted. Her heart pounded a little harder. She swore he could hear it coming out of her chest, so she quickly replied, “I guess that’s ok…”
Her pride wouldn’t let this young arrogant wizard know that she was deeply hurt by his indifference, so she persuaded herself it was her own immature mistake for letting emotions get the best of her. After all, didn’t Sirius just say that James liked her? He was the most popular wizard in school. She actually did have a crush on him. Not Sirius. So what had just happened!?
Sirius stood up from the desk, heaving a big sigh. Good, I didn’t have to show all my cards, he thought. Lily watched as he reached down and checked his pant zipper, brushed his dark hair back with one hand and started towards the door. He was leaving. When he grasped the handle, he turned back towards her.
“Alright, Evans. Uh.. If it’s any consolation to you, Snape’s a dope for calling you a.. well, a you-know-what.”
She sat in silence, taking in his words.
“And.. um.. if you do end up forgivin’ Potter and giving him a chance on a date,” he paused and shifted his weight, "I’ll make sure he knows what a catch he’s got.”
With a click of the door, Sirius had left her alone in the study. Lily stood in silence before falling to the floor, tears starting trails down her eyes, feeling as if her heart had been torn out of her chest.