Think it is harmless as Anniebrooke says. If you find your partner can't please you because it's not the same as you pleasing yourself, then you'll just show them how you do it. But overall, this is not unhealthy behavior.
It won't hurt anything. If you were wasting a lot of your day doing it, or running off to have fun alone in preference to having sex with someone else (or in preference to living life in general), it might be problematic. But otherwise it's certainly not bad for you or your sex life, and can even be somewhat good for your cardiovascular system if you get excited enough. :-)