FYI, here are some of the tags for this story on AO3:
Romantic angst, Emotional hurt/comfort, character study, angsty schmoop, implied sexual content, consensual kink, BDSM, light dom/sub, mild S&M, Dom Gamora, Sub Peter Quill, songfic, guilt over corrupting a good person, love, trust, comfort/angst, light/dark, dark and light themes, comfort, wholesome angst, feel good angst

Song: Down Side of Me by CHVRCHES

Keep you away from the down side of me

"Peter, I'm dangerous. I could hurt you," Gamora growled, making it clear she was talking about more than just sex.

The fact that she was now on top of him after just tackling him to the ground, snarling out her warning as she kept him pinned by the wrists made it seem pretty sexual.

In truth, it was pretty sexual. But it was clearly about more than that too.

Gamora had never been the most selfless person, but she was trying. She was trying to do better, and to be a good person. But he made it so damn hard.

All the incessant flirting was just picking at her self control, and apparently that suggestive comment he had just made 15 seconds ago was her breaking point.

She was trying to be a good person, and he was just so tempting. All she wanted to do was ruin him, and Peter kept offering himself to her, cause he had no idea what he was getting into.

He had saved her life. She owed it to him not to destroy his, no matter how many times he offered himself to her out of sheer ignorance and naivety. He didn't know any better. She did.

This wouldn't end well for him.

She could see it in his eyes, as she snarled out her warning. Tried to frighten him off, because he's so bright, and she's dark as night, and she couldn't ruin the brightest thing in her life. She'll take all his light if he lets her.

And that's what this was about. This warning. The one that she growled into his face after tackling him to the ground, vicious and snarling so he'd get it through his head- her warning him.

Don't let me take your light.

Peter breathed out, steady, measured, and controlled. She knew he understood. The full weight of what she meant. There was a resoluteness in his eyes, as she stared down at him, he stared right back.

"I trust you," he said, sure of it.

"You shouldn't," Gamora snapped at him, digging her fingers into his wrists. He flinched slightly at the initial pain, a body reaction to suddenly having someone's nails digging into your skin. His eyes dilated quite beautifully.

There wasn't even a flicker of doubt on his face, no hint of uncertainty.

"I know," he responded. Simply. Like it ever could be that simple.

She squeezed his wrists harder, her nails digging into his flesh. He didn't flinch this time. Didn't even react.

"Why then? I'm going to hurt you. I want to hurt you."

"I don't mind," Peter told her, an eerie settledness about him, that was only unsettling to her. And frustrating.

There was something solid and resolute, a challenge in his eyes, rising to the occasion and meeting the fire burning in heres.

"I'm going to destroy you one of these days," Gamora said, baring her teeth, voice filled with rage and something much deeper, something much more violent. She dug her fingers into his wrists like claws, hard enough to draw blood, so maybe he'd get the fucking point. She didn't know if she was warning him or threatening him at this point.

"I know. It's okay. Do it," he said slowly, raising his head up, elongating his neck and exposing his throat to her.

Her grip momentarily slackened on him in surprise. She was stunned.

"Gamora. Please."

And she knew she was evil, and she was going to pollute his goodness, she knew this, she was going to ruin the best thing she'd ever had. She was going to destroy him.

She was going to lead him to his end.

She knew this as she dipped her head down and bit his exposed throat, hard. When she marked him as hers.

Peter moaned when she twisted his arms up high enough to hurt, and she was certain she was going to be the death of him some day. She was going to ruin him.

So she continued. This dark and twisted love that she knew would hurt him. A need and want, a selfish love. That would swallow him whole. Devour him.

She does hurt him. Makes him bleed.

She had her ways.

She hated herself when he was tied up to the bedpost, no longer making noises with every lash of the whip that cracked on his bare back. Just took the punishment from her.

When she was done with him that night, Peter collapsed on her bed, face first. There didn't appear to be any blood from all the lashings she gave him tonight though.

Just angry red marks on his back that had to sting.

Gamora sat beside him, grazing his back with her soft fingertips, and he hissed at her touch.

"Why do you let me do this to you?" She asked for not the first and certainly not the last time.

"Cause I want to," Peter replied just as easily as ever. That was always his response to that question.

"You want me to hurt you?" Gamora rephrased, making it sound as absurd and messed up and insane as it honestly was.

"I want you to do this to me," he corrected.

"When are you going to get it, Starlord? This won't end well for you. I will cause you more than pain. I won't leave you a wreck. I won't stop until there's nothing left of you," she told him, surprisingly calmly, like they were just chatting about the shapes of the stars in the sky, or other banal facts of the world.

"I'm okay with that," Peter sighed out deeply, turning his head to the side. "I want you. I want you to want me. I want you to want me this way too. The way you do. I want this."

"This isn't a good love. It's bad. It's very bad. I wish you wouldn't let me keep you like this," Gamora said, stroking his hair.

Peter smiled. "Yeah, no need to get all existential dread over yourself. Hate to break it to ya, but you're not as bad as you think. Not some evil harming influence, sorry," he smirked, and she opened her mouth to protest, but he spoke first, and beat her to the punch.

"Make me happy, so you can't be all that bad, right?"

There was such a warmth and light and laughter in his eyes when he looked up at her, and it made her go speechless, her heart feeling strangled in her chest. In a way that wasn't entirely unpleasant.

"Besides, it's been a year- two? You've been fucking me for awhile, and I'm still here, despite what you say. Not ruined or destroyed or whatever. You think you would've ruined me by now, huh?" Peter asked, clearly a rhetorical question. "Sorry to say, your love's not a corrupt thing, Gamora. Don't get me wrong, it's hot when you treat me like innocent Bambi and you're the super hot lioness that's gonna devour me. But you'll see one day. How good your love is. How good it's been this whole time. I don't love bad people, Gamora. And I love you more than anything. You'll see. Promise. One of these days I'll make you see how good you are. How good your love is," he told her, a dreamy sort of contentment on his face as she continued brushing his hair.

She doesn't know how she hasn't made him so cold yet.

How he still has this warmth. Burning brightly, all for her.

She doesn't understand how he can still have this warmth for her.

He should have grown cold long ago.

Not… not this.

Not a light burning brighter, lighting up her darkness.

I believe, I believe
And tell myself to think forward
I will show I believe
And I hold you up and know that you're all I see in the light
And never do what I used to

Keep you away from the down side of me
You can keep me a drip of the light that you see
I believe that you're all that you said you would be
If I keep you away from the down side of me

You can keep me a drip of the light that you see (only if I could see)
I believe that you're all that you said you would be (only if you could see)
If I keep you away from the down side of me (Only if I could see)

You can wrap up your hopes and release them to me (Only if I could see)
You can keep me a drip of the light that you see (Only if I could see)
I'll believe that you're all that you said you would be
You would be
You would be

And I believe, I believe
And tell myself to think forward
I will show I believe
And I hold you up and know that you're all I see in the light
And never do what I used to
And never do what I used to

~Fin~

AN: this actually didn't start out as a songfic. It wasn't until after I'd written this that I was listening to the CHVRCHES album and realized how well it fit. Seriously, the working title for this fic was 'dark romance' (cause I'm cliche like that). The song line worked out much, much better.

You can just find it on youtube. My favorite version is 'CHVRCHES Down side of me (live)'- it's so haunting and artfully stripped down into like an acoustic version of the song, but if you're more into techno you might prefer the album version over it, still lovely and haunting- both versions are on youtube. And, of course, that's where the lyrics at the end of this fic are from.