lasting longer? try to go ahead and get him off and let him stimulate u and arouse him at the same time. if he can last two times then he'll be longer the second time.
just try and see if he can go two times. just let him get off and arouse him again while hes stimulating u. it might help bc he'll be with u longer. also, i agree with some of the info above. being relaxed will help. u might be thinking that ur a burden to ur boy or something like that. and believe me ur not, he wouldnt be with u that long if he didnt want to help u. just relax and clear ur mind and think about having an O and thats all. concentrate on the feel and stuff like that. just be calm.
hope this helps. best of luck.