It took me a long time to figure this out, under a lot of masturbation and meditative masturbation I have found many ways to increase how long I can go, but not forever... Until about a week ago.
There are two ways to do this, one way may work for one person, another way may work for another person...
One way is... when you're on the verge of ejaculating, instead of trying to hold the semen in by tensing your groin muscles, keep going, but relax your penis instead. For some reason this seems to stop it.
Another way, the way that allows you to still ejaculate, is... When you're just about to ejaculate, to the point to that even if you stop, you will still cum, relax your penis completely. You'll ejaculate, but you will still be able to keep going on afterwards.
Relaxing is the key.