[Civvie]

I also have problems cumming for a long time. However, unlike other advice, the key to helping me cum during sex was to masturbate WITHOUT porn.

You lie down on a bed or somewhere comfortable without any distractions. Then you masturbate, no death grip and no need too fast. Then close your eyes and search for a fantasy in your mind that will make you cum. This is trial and error. It took me some time till i found out my go-to fantasy that will regularly make me cum (don't want describe into detail but it involves my girlfriend stripping in a certain location).

For starters, i would suggest watching a bit of your favourite porn to get your blood flowing and your mind dirty. Then stop watching but continue to masturbate and find your fantasy in your mind. If you go soft, watch the porn again. If you cannot cum no matter what, then take a break. When you become extremely horny again due to the lack of an orgasm, try again.

Then use that fantasy during sex in your favourite position or a position that lets you control your rhythm easily so you can concentrate. Before that, get into foreplay and enjoy your favourite parts of your partner's body to REALLY get into the sexual mood. Listen to her moaning, look at her nipples/breast/pussy/face/some other favourite part, congratulate yourself on fucking a hot girl AND most importantly, play out your fantasy. If it grows soft, pull out your dick, relax and look at the girl's body from another angle and allow it to erect naturally. Then try again. Be determined.

It worked wonders for me. Cumming is all in the mind. If you do it regularly, you only need a few weeks, maybe lesser.

TL;DR : It is all in the mind. Masturbate and cum using your mind, not porn. It is a skill, keep at it and you will get better.