Helping him finish?

This is probably an odd one 😅 but whenever me and my bf have sex, he takes a long time to finish, we do different positions an he normally finishes if I’m on top. A lot of times it slips out an he gets frustrated an it goes “down” or I get a little tired while being on top because it takes long. Does anyone have a partner that lasts a long time, is there anything you do to help them finish?

I know normally you do want someone to last long so I’m not complaining but I’ll finish so then I’m also not as turned on by time I try to help him finish but even if I don’t finish first it just takes a long time an I want him to finish but idk what to do, I’ve never had this problem with a partner b4