Girlfriends Younger Sister

My current girlfriend who I love has a adult younger sister and I’m crazy about her. Ever since I laid eyes on her, just wow.
I want her soooo bad it’s ridiculous. She’s so pretty, has massive tits and a huge ass. I constantly check her out at every opportunity I have, to the point of almost getting caught. I’ve seen her in a bikini and it was so hard not to get a full on erection in front of anyone.
I always thick of her when I fuck my girlfriend and always wank over her pictures and she makes me so hard and cum so fast. I want to constantly breed her, ydek. She was staying one night and a managed to sniff her dirty underwear and it smelt like heaven. I’ve even had a wank sniffing her shoes. She lets these huge farts out too that I wish she’d sit on my face and do. Just anything of her makes my cock solid. I’d risk everything to just fuck her once. I fantasise about her all the time and wonder what scenarios I could approach her but it would ruin my life and I’d lose everything if it didn’t go to plan. What are some ways I could sneakily approach her or make her think about me in a sexual way? Also, I need to get hold of some of her nudes or used panties again. Tips?