Id fuck the shit out of your gf. She hot as fuck.
She's hot as fuck..
Easy, subtle way is to get her boozy (if possible) and horny then ask to roleplay with her pretending you're another guy, an ex, or just some dude she only knows of and call you his name.
Or roll the dice and ask if she'd be interested in a threesome with another dude, you don't have one in mind just curious and let that boil for a bit. If it doesn't go well just say you're sorry you get kinky when horny and all is done.
haha bro you wish she was your gf