How do male porn performers come more than once (serious question)?

You are not masturbating properly.  Hire a more experienced older man to help you with your technique.  Your instruction should include a lot of "hands on" lessons.

Porn is fake.

Thirty minutes to an hour of "love making" could have taken two or three days to film.

Editing is a porn producers best friend - wasn't enough **** in the scene - just edit in some more.  

Serious answer.  

Now you know why there are so few male porn actors in the business.  Serious answer.

There is some movie magic that happens, like shooting the same scene from multiple angles to make it look like multiple scenes, or re-using the same footage in other scenes (it's porn, the audience won't care), but porn actors are a special breed.

To get a job as a porn actor, a guy has to have an excellent physique, an above average sized weapon, and Shaolin monk-like control.  He has to be able to get wood on command and keep it stiff, even after an orgasm.  Very few guys can do that, which is why you see the same guys over and over in porn movies.  On top of that, he has to perform the act in the most ridiculous pretzel-positions, with a camera operator usually right under his nose, and he has to look like he's enjoying it the whole time.

When it first came out on the market, a lot of porn actors simply got a prescription for Viagra.  But that stopped fairly quickly, as soon as the life-threatening side effects of abusing Viagra became known.  

They do it with the magic of editing.
Remember... porn is still part of the movie industry.

Movie magic.    

They shoot multiple scenes.  The guys don't really last that long, either.  They add them edit together in post production to make the video look how they want.

they work days to put on a single movie. Lot of fakes... never blieve a porn movie. well, to any movie.

thats why only a few can perform

Viagra helps but it is just something they can do. Remember, porn is fake. Everything about it is fake. If a guy can *** more a day, he gets paid more. I was young and in love and I came 17 times in one night. I don't think I could ever repeat that. 

If you watch carefully, when the male cums the first time, you usually see his whole body and face as he ejaculates.  When he cums the second time all you see is a penis shooting ***, most of the time it is another males penis, that looks like the first actors penis.

I think you'r under the illusion that all you see on a porn video is reality.  Whilst that may be a wonderful dream, it just isn't so. 
Very few , if any of those incidents, have the sporttangu that they portray. If you look very carefully, you will notice that the momentous enjoyment that would (or should) occur is totally absent, and some very clever editing produces  the final finished production.  Its just a commercial exercise, and  in many cases you will notice that the actors look as bored as hell.  You could  often see more genuine passion being experienced whilst they eat a meat pie. 
If it gives you pleasure, then enjoy the image, but do try to retain your sense of reality. 

They obviously have a bigger sex drive than you have.  (You can only ejaculate ONCE?  I feel sorry for your sex partner.)

Those porn's are filmed over a week or more, then they are edited.

Because you watch too much porn.
Soon you will have ED and wont be able orgasm even once.