My Step Father

Before anyone says anything, I know I'm a highly sexed nymph. And I also know it's probably not appropriate what I'm trying to do.
What I'm talking about, is wanting my step father Robby to fuck me.
I know for a fact he likes me in a sexual way. I also know he has a large cock. I know this because I've watched him and my mum fucking a few times. She's never seen me watching, but Robby has and hasn't told my mum I was there.
These past few months I've been teasing him nearly every day, by flashing him my breasts, pussy and arse at him. His reaction is nearly always the same, he gets a hard on and then tries to hide it.
Only a couple of weeks ago I caught him masturbating after I'd flashed him my pussy, sat opposite him.
A few minutes later he was on their bed stroking his cock, whilst using a worn pair of my knickers to sniff.
Robby didn't see me watching him, but he did hear me groan when I watched him cum into my knickers.
Since seeing him a couple of weeks ago, I've purposely left him used knickers which I'd wiped my pussy with, after I'd masturbated.
Every time he's used them to wank and cum all over them. He's then put them back into my wash basket.
I'm very sexual myself and have had several boyfriend's, all of whom have enjoyed fucking me. The reason I finish with them, is I'm always looking out for the next best, more experienced lover. And I know Robby and I would be perfect together.
All I have to do is convince my mothers husband, I'm the one he should be fucking.