Run

To me, this song is about the dilemma of being attracted to a person that you should not want and therefore telling them to just run away before things get even more messed up. Right in the beginning of the song, the speaker already admits a certain desire for the other person; a feeling which he calls evil for some undefined reason. Possibly, there is a third person involved whose feelings could get hurt, which is why the speaker feels guilty about the situation. I would guess that it is about a flirt they have, maybe at a party (since "the moon invites the madness"), which started out with joking and teasing ("just having fun") but eventually reached a point where things got serious, so that the speaker finds himself with the metaphorical gun in his hand. Probably, their flirt has become so intense that he knows he will give in to his desire and the only thing that could stop this development would be for her to get away, because he doesn't have the strength. In any case, the speaker already feels guilty about the whole situation and wishes he had been a better/stronger version of himself ("How'd I become so ruthless? / Where is the other me?"). He is left to struggle with his passion as well as with the self-contempt he begins to feel (and which surfaces in the strongly negative expressions such as "demons", "the worst", "evil rages", etc). It all sounds very desperate to me but at the same time so relatable, because everyone has desires that don't conform with social expectations, so we try to suppress them and when we don't succeed, we end up wondering why we were acting in such a poor way.