Masturbation CANNOT make you blind, or cause any other physical ailments. You are young and single, and it is not doing you any harm.
When you are in a relationship, it is still OK to masturbate and it doesn't mean you won't be able to have sex with your wife. However, as you have noticed, things change when you are in a relationship. Expectations of a "real life" sexual experience with a woman need to be managed. That means that you don't want to turn to pornography as your expectation of a "real life" sexual relationship, and you want a good portion of your sex life to focus on sex between you and your partner. But there's nothing wrong with masturbation, unless it becomes very time-consuming or you become obsessed with it to the point where it is affecting other aspects of your life.
I agree 100% w/ CurfewX - masturbation is not harmful in any way, unless it becomes an obsession. The only real issue is that many guys get used to their own ‘technique’ & are used to reaching orgasm very quickly this way. There have been other discussions here on MedHelp about this issue - what you can do is practice the ‘start & stop’ technique while masturbating. When you feel you’re getting close to orgasm, stop & wait a few seconds, or up to a minute, then resume. Once again, when you’re getting close, stop & wait a bit. You can do this several times & eventually, go ahead & allow yourself to ejaculate. If you practice this for several weeks, you will find you can learn to extend the time before you ejaculate. This will help you when in a relationship. Keep in mind that women usually need a much longer period of stimulation to orgasm - and usually don’t with intercourses alone, so give her a lot of manual or oral stimulation. Also, as CurfewX says, you don’t have to stop masturbating when in a relationship, but one bonus if learning to hold off orgasm longer is that the feeling will probably be more intense when you finally do, and you’ll probably ejaculate a larger volume as well. So there are some real benefits to using the start/stop technique whether alone or with a partner.
Once again - do NOT believe anyone who tells you these myths about masturbation - you won’t go blind, you won’t run out of semen, it won’t ruin your sex life with a partner, it won’t cause ED, etc. It’s really sad that so many people believe these outdated myths that have all been proven completely false by modern medical science. In fact, virtually all Dr’s nowadays regard it as a normal activity that is not harmful in any way & in fact believe it to be beneficial.