Giving my GF a bigger cock for the first time [cuckold]

I've been thinking about the thought of cucking my GF for many months now, when I get horny the thought of it turns me on so much, I 24 (M) have a 5 1/2" cock and all though my GF(24 F) seems to be satisfied by me I've always wanted to see her get fully pleasured by a real cock something long and thick. Seeing her getting satisfied fully would turn me on so much and since I don't have the cock to do so the thought of cucking her turns me on so Much, I've had cock/wank tribs done of her and honestly seeing her wiry these big cocks has made me fantasise about it even more. We have been dating for just over 5 years now and this is a new kink I have recently developed and I am scared to tell her as I am unsure how she will react to it, recently after nights out when we get home and have sex I tell her how good she looked that night and how hot it was seeing guys try to flirt with her and try buy her drinks, telling her it made me horny watching them try to pull her and she gets so horny when I tell her this however I feel like it's quiet a big jump to tell her I want to watch her get fucked by another man lol. But this weekend we are booked to go away for the weekend and to treat her I have bought her a naughty little outfit and a few toys spice things up. I've ordered a blind fold so I can tell her to lay back and relax whilst I take great pleasure in satisfying her in ways i have never been able to before, mostly with help by the (main event), The main event being a 10" cock sleeve. It arrived today and honestly when I took it out the box I got hard thinking about how excited I was to use it on her and see her reaction. I've also order a vibrator, lube and some handcuffs to help elevate this experience. I'm hoping all goes well and this brings out a new side not only in me but in her to and maybe one day she can have a real big cock inside her one who really knows how to use it and give her it properly.