You would start to have more and more nocturnal emissions or “wet dreams.”
You libidinous energy, having lost it’s major outlet would get sublimated. This means that you use all that energy for some other purpose. You’d become a poet, a fascist, or a motivational speaker; maybe if you have been masturbating a lot, you’d be all three.
Since masturbation reduces stress, elevates mood, and promotes quality sleep, it is likely that you would feel anxious, depressed, and fatigued.
You would experience more frequent and more intense arousal when the body senses the possibility of actually having sex. That is to say, you’d be popping boners all the time. All an attractive person would have to do is smile at you and you’d pop a painful, aching erection.
If you lose your penis, your testicles will still make sperm, and it will still build up until it needs release. If you have no penis, you obviously can’t masturbate the usual way, but people in this extremely unfortunate condition have found ways to stimulate themselves until they release their sperm. Or, it is simply released during sleep in a wet dream. The penis extends into the body a few inches, and the internal shaft can be stimulated even if the external shaft is gone.