how do i convince myself & 21gf to try cuckolding in real life (never tried first time for both of us but i need guide on how can i make it happen how do i manage a staranger to agree to my terms even after i convince my gf )

i am 21M i am huge cuckold fan specially Voyuer type i ahve confessed about my fantasy to my gf but she is too scared to try for real. To some what fullfill my fantasy she would write me confessions type story of us and a stranger be intimate like threesome with different senario in different stories she would blow me while i was reading the story she created . But i am really scared to try these things special with strangers. i prefer the stranger to not have any feelings or intrude our couple space after the deed is done help me guys