>>936220706It completely depends on the girl, she needs to be pretty open minded to begin with.
My experience was it took about 2 years since she mentioned she wanted to get dpd, I was bi so she was more turned on by me sharing a dick with her rather than blatantly her cucking me. Eventually we had a threesome with another guy, it evolved into me taking more passive role (holding her legs open, lubing her up, etc).