You know it is wrong. It is so, so wrong. You don't even know him, at first. How evil must you be, to cheat on the man you love with his best friend's little brother? But you do, and it's so hard. You hate it. You hate the secrecy, you hate the confusion, you hate the feelings you just can't avoid, and most of all you hate the guilt. You know that holding hands under the table, stolen kisses and hastily cast concealment charms is not really a relationship. You ignore it.
You wouldn't even be in this situation if Sirius hadn't found the one place in the ancestral home that wasn't warded against mudbloods – against people like you. It was the basement trapdoor, as it turned out. The servants' entrance. It makes you feel downtrodden, not even worthy of a proper door. James doesn't understand, but Regulus does. Your Reggie. You know he's not even yours, really; he told you about his arranged marriage to Molly Prewett after your first kiss. He understands, because he is as downtrodden by his family as you are by society.
Fidelity has never been your thing, really. You love James, you really do, but you just feel this irresistible pull whenever you're around Regulus. At least you know your type – tall, handsome, black-haired. You suppose Severus would have fallen into that category too, before he called you that name. You wish Sirius didn't get on quite so well with his brother, didn't include him in your little gang. Not quite part of the Marauders, but on the edge of the circle, wedging his foot in the door. You're like that, aren't you, Lily? Always on the outside.
Not even your relationship with James is good anymore. It was a secret pleasure of yours, when he asked you out time and again. It made you feel special. Now, there is nothing. You wanted some excitement, some energy – and Regulus gives you that. The stolen moments in empty classrooms, the sneaky trips to the Forbidden Forest, the brushed hands as you pass in the corridors – they give you a thrill, a rush of adrenaline you never get with James. James is safety; Regulus is risk. You need both, but truly love only one, and you know it will be him you stay with. You can see your future mapped out in front of you and you want it desperately, but deep down, you want to prove them all wrong and show them that maybe, you aren't just stereotypical Lily – brave, faithful, honest, good.
This thing with Regulus – this is your hidden victory, this is your defiance of everyone who thinks they know the real Lily. Only Regulus knows the real Lily, and you hate that. You hate it because you are destined to be with James, yet you yearn to be with Regulus. Honestly, the concept of forbidden love enraptures you more than he does – Slytherin and Gryffindor, pureblood and muggleborn, dark side and light side. You know you will have to end it eventually, but for now – for now, all you want is to enjoy being the real Lily.
This was written for the Out of Your Comfort Zone Competition with the prompts Regulus/Lily and Fidelity, and the If You Dare Challenge with prompt #629 - Guilty Heart.