I believe sexual stimulation helps your penis strength, but it is the ejaculation which depelets you. Here’s a simple way of thinking about it which I’ve shared several times on different threads:
The pressure built up in your penis as you gain an erection serves a couple of biological purposes. First, it allows you to have an erection which reaches deep into the vagina. Second, during ejaculation, the pressure is released for the purpose of shooting your semen deep into the vagina. Obviously, our semen wants to reach the egg, and the whole build-up of pressure revolves around this purpose. Now, once you ejaculate, the pressure is lost because the biological purpose was satisfied. Simple as that.
If you want to gain amazing sexual power, keep on masturbating and having sex but ejaculate only on the rarest occasions. This solves so many problems, and you’ll never understand until you step through the doorway. It might not end up being your thing in the end, but it’s worth a shot for everyone out there.