Learned this from a skinny, no butt girl but in a different context. She's 23, has a really cute face, and small boobies.
After the first round of my fuck routine, Joy (that's her name) wanted more fucking and does not want any oral sex. But my dick was already limp and I figured it will take some 30 minutes to one hour before I can get it hard again. I don't like blowjobs either.
The amazing thing that Joy did was to get on top of me and used my dick to masturbate her pussy. She rubbed my limp dick on her clit and her still wet labia. After a few minutes of that, I was hard again.
Fast forward to the present. When my dick gets limp or can't get hard (must be the age somehow), what I do now is use Joy's technique to get my dick hard. I masturbate the girl's pussy with my limp dick until it gets hard.
Works for me, it might work for you.

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