Do not do it ! What is more important : the penetrative ("top") partner's short-term small increase in pleasure ? OR - As the receptive partner ("bottom") - your own long-term health, safety, & well-being ??? (receptive partner "bottoms" are at a much, much higher risk of acquiring an STI due to micro-tears etc) [ if it's love, they'll wear a glove ] otherwise, if they refuse : kick em' to the curb. YOU DESERVE BETTER