You don't need a girlfriend. You need to learn how to control your body and mind.
The sexual energy is creative energy and must be utilized as such. Physical exercise helps a bit, but there are more effective ways to transmute the energy. For instance, you can perform prayanama all day long if you want. The rites for rejuvenation also help.
Most effective of all is to be using that energy as it should be: to change. If you are observing yourself continually all day, and meditating every day to comprehend your behavior, you will require every bit of energy you can muster. Meditation — real meditation — requires a lot of energy.
However, if you do not meditate, or if you allow lustful thoughts or lustful gazes towards others, that energy will build until it hurts you.
"Do not worry; cultivate the habit of being happy." - Samael Aun Weor