Any type of rigorous physical activity (sexual or otherwise) can desensitize the nerves in the body part that is undergoing the activity. Why do you think porn stars retire so early? You need to control your mastrubation. Cut back from twice or more a day to once a day for a week, then cut back again the following week to every other day, and so on until you are only mastrubating once a week. See if that helps your ED and/or sleep problems. As for the worrying about relationships in the future, you need to relax. All of that stress is not good for anyone. If you cut back on the mastrubation now, only time will tell if it helps reverse the insensitivity.
Was your masturbation to Internet porn? If it was then it's likely that you have desensitzed your brain- not your penis.
Internet porn can become an addiction, and with all addictions the brain changes, or adapts. It does not matter if the addiction is to a substance or whether it is a behavioral addiction, the same brain changes result.
Today's internet porn is nothing at all like our ancestors ever encountered, with the constant novelty and genres of extreme porn. Unlike yesterday's Playboy, Internet porn overstimulates the brain structures responsible for libido, erections, and addiction.
Brain changes include a drop in dopamine receptors in the reward circuitry. Reducing the amount of dopamine receptors decreases your pleasure response to "normal" stimuli. In other words, real-life sexual partners and previous porn won't excite your brain enough to get your penis going. Turning on dopamine receptors is how you get turned on.
Here are two excellent presentations, by a science teacher, on the effects of pornography on the brain. They are non-religious, non-judgmental, and science based.
Erectile Dysfunction and Porn:
Your Brain on Porn - Porn Addiction:
Here are two articles on porn-induced ED
“How I Recovered from Porn-related Erectile Dysfunction”
As Porn Goes Up, Performance Goes Down?