I like being like this

These feelings are triggered by specific stimuli. That is not your initial, usual state of mind. It is a response of yours in certain situations. This means that your inner personality is the "good" one, while these internal swings do not define you. So there you have your answer. The "evil side" is actually a deviation from normality, from your own standard. Now that you have this information, you can start preparing yourself psychologically for confronting the foreign attitude that does not represent you, but keeps invading you, in order to protect yourself. Find ways to control yourself and resist to these invasions. Many people suffer from these, so we have developed lots of possible solutions.

You must know that these feelings are temporary and consume a lot of energy, since they do not belong to you. You may feel tired after thinking in that way for too long. This means that you cannot live this way and you cannot permanently switch to the "dark side", since it literally drains you of energy and soon enough you will return to the inital state. If you want to select one and stick with it as much as possible for a stronger sense of identity and a peaceful state of mind, your only realistic option is the "good side", since this does not consume energy and does not depend on limited resources. I also suggest you the same. You will need the energy for better things which bring you more benefits, and you will notice that this energy starts being consumed as soon as the switch is triggered. For more achievements and a happier life, I recommend sticking with this one. Also people around you will suffer from this if you do not learn how to control it, and soon enough it can lead to disaster. There are lots of people out there making bad and irreversible decisions and regretting them. It also "feeds" the "dark side" and you have less control over it. Shortly, don't let it take over. It damages you.