The main causes to premature ejaculation are:
I can help you with the physical side of things, if you have performance anxiety then I strongly recommend you consult with a sex therapist.
So let’s start.....
Are you able to recognize both of your pc muscles separately?
The first one is between your asshole and your penis (scrotum) and the second one is between your asshole and your tailbone.
When you pee you use the first one, when you poop you’re using the second one.
To last longer in bed, you have to get better at the second one; a lot of people overtrain the first pc muscle and it can actually cause more trouble because it creates an imbalance
You have to train those muscles separately so you gain more control over them.
Start by pulling inside (contracting) and hold it for a few seconds, then push it out (release) for a few seconds; this will both stretch and strengthen the muscle.
Do the same exercise for the first and then the same for the second. When you figured everything out, next step...
Now you should start to edge WHILE practicing those muscles, it will improve results tenfold and will make you used to the sensitivity as well
Here’s a video I practice to while exercising my pc muscles: https://www.pornhub.com/view_video.php?viewkey=ph5b2f925589611
If you practice once a day, you will see results in under a week. If you get penile skin irritation, put coconut oil on your dick and start again in 72h.
If you want to practice with your GF, make sure she’s on top because missionary makes us use a lot of strength from our abs/legs/back to maintain the position; it makes it much harder to control, especially for beginners.
Good luck !