It's almost certainly a mental thing. I think too many guys get caught up either in just pleasing the girl, or they're not thinking of sex the right way.
What I mean by "right way" is that too many men (and some women) are far too analytically and rational about sex. Especially if you've had a problem with pron, it can teach you to think of sex as essentially mutual masturbation. In addition, many men don't have sex even for pleasure or emotional connection...to a lot of guys it can be simply about ego and power.
Sex is about emotion, connection, and losing yourself in it (unless you're just trying to get off in a warm hole...in which case a fleshlight or even your own palm will accomplish much of the same without the work and risks).
Next time you are having sex....slow down. Shut off your rational mind and focus on what you are experiencing and purely living in the present moment. Rather than worrying about when you will c*m or whether or not you are having fun or what the girl thinks about you or if she is having fun...simply disconnect from everything yet at the same time plug yourself completely into the present moment and let your senses become amplified. Focus on how good it feels to touch and be touched by a woman. Look into the girl's eyes and feel something with her rather than just trying to get off (or get her off). You will find that letting yourself become lost in her will naturally progress to orgasm (and hopefully simultaneous with hers).
Stop making sex a checklist with an end goal of any kind. This is the thought process of far too many guys:
O) Okay first i makeout
O) okay now i play with her boobies and her pu$$y and touch her a bit
O) Sweet, time for a BJ! man, i hope she doesnt just stop after a few minutes
O) Hopefully she's turned on enough for me to stick it in. Okay, it's wet, cool. Time for the sex.
O) Okay she had her orgasm and it's been a minimum of 10 minutes which means it's okay for me to get off without looking like a premature chode. Change up a position or two so she thinks i'm a sex masta and know what i'm doing
O) Yes, time for me to finish. OKaaayyyyy ARGH! Humph. Hooh!
O) Yessss I just had sex, i'm so cool, i'm going to tell my friends and post online anonymously about it.
O) Hmm i'm hungry, hope she doesn't wanna cuddle with me for too long
It also begs the question of whether or not you have a connection with these girls. banging girls is cool and fun and your buddies will think you're a bad a$$ if you sleep with tons of girls...but let's be honest here: if you're simply trying to get laid for the sake of getting laid and because SoSuave or some PUA told you to get laid as much as possible, then the sex probably isn't going to be that fun. Believe it or not connection is extremely important for sex. Now i'm not saying you have to fall in love to have great sex. However, it's important to find a girl that turns you on and that you feel something for, rather than just seeing her as a warm hole. Even for ONS's...there are girls whom i just took home because i wanted to have sex that night...and then there were girls with whom I felt a huge sexual attraction with right off the bat, and sex was just a natural progression of how attracted we were to each other.
Also...are you drunk during these one night stands? That's a huge factor. It's very easy for me to come usually (and even too easy occasionally), but if i'm drunk i often wont be able to.
