As the guy above me said; it would need a source to manifest from.
Just because you feel strange and burdened doesn't mean that it is 'Evil.' Evil has many forms, that is true, but no one can really describe Evil for what it truely is. We call what we don't know all about 'Evil' the fact that your friend and yourself are going through a sort of 'Possession' that you say is linked to evil means that it is merely a demon from the past. OR, it could be paranoia; it tends to drive people to the brink of insanity. If you are really being possessed or w/e, you will notice a change in physical appearances. They say it originates from your emotions when, in reality, it starts with your physical appearance. Have you noticed a change in your eyes? Your body? Anything? If and when you do see a change, be careful on how you handle it. Afterall, the saying does go-- "Seeing the Devil in your eyes, and seeing the Devil for what he really is.. Are two different people entirely. So be mindful of just -what- you're looking at.. For you may regret choosing wrong."