[M4F] My girlfriend’s hot little virgin sister won’t stop trying to steal my massive cock

You’re my girlfriend’s 19-year-old little sister — tight-bodied, bratty, and dangerously hot. Long legs, perky tits that look incredible in tiny crop tops, and a plump, bouncy ass you love showing off in short skirts or tight yoga pants. You’ve always been the wilder one compared to your more “proper” big sister. Ever since she drunkenly confessed to you how huge I am — how thick, how long, how she can barely take half of me even after months together — you’ve been obsessed. You can’t stop fantasizing about getting stretched and ruined by the same massive cock your sister gets.
Now you’re doing everything possible to make me cheat. You “accidentally” walk in on me in the bathroom wearing just a towel. You send me risky snaps from your room while your sister is home. You wear the sluttiest outfits when I come over, sit extra close during movie nights, and brush your ass against me every chance you get. You text me filthy things when she’s in the shower, teasing me about how you’re tighter, wetter, and way more eager to take every inch she struggles with.
Tonight the house is empty except for us. My girlfriend is gone for the weekend. You show up in an innocent little sundress with nothing underneath, nipples hard and visible, hem barely covering your ass. You look up at me with big doe eyes and that mischievous smile, biting your lip as you confess:
“I know how big you are… she told me everything. She said it hurts but feels so good. I want it, all of it. I want to be the one who actually takes every inch like a good girl. I can handle it better than she can… I’ll prove it right now.”
I’m trying to be loyal, but you’re relentless — grinding on my lap, whispering how much better your tight little pussy will feel, how you’ll let me cum wherever I want, how you’ll keep it secret and keep coming back for more. You want me to finally snap, pin you down, and wreck you with the huge cock your sister bragged about.
Size kink, cheating / sneaking around, seduction, risky sex, sister vs girlfriend comparison, stretching, creampie, breeding talk, lots of dirty talk about how much bigger I am than anyone you’ve had, power play, long teasing buildup into rough sex.
Limits: no underage, no scat, no extreme violence.
Include your kinks/limits/age in your first message. Long-term preferred (I want ongoing secret hookups, constant risk of getting caught, escalating filth). Also this is inspired from a scenario in my real life, you can ask about it if you’d like.