Protip: use two fingers in your partner’s bottom so you have him more opened up. Then stroke his prostate with your fingertip, softly at first (almost a tickle), increasing pressure as you go. The additional finger will help give you freedom to move, which he will appreciate — sometimes going in and out causes a bottom to think he might have to use the bathroom, while stroking without moving in and out stimulates the target area better.
Every time I do this to her, she can’t stop coming. We did it twice last week, and it was amazing.