The person who is speaking is/was a best friend (or a bf/gf/spouse) who happens to be dead but will always be in your mind. (Although they could be alive too.) They realize that you had been alone without them all this time.
It could be an evil enemy who's taken over/trying to take over your mind. Or they're just threatening that they'll always be there in your mind. (Like the theme in the movie, "Cat's Eye" with the song "I'll Be Watching You". Or if you've recently seen that cartoon, "Teen Titans", when Slade was in Robin's mind, and no one else could see him except Robin, in which he was perceived as going crazy).
But I like to think of it as my best friend with theory #1 more. Although I can see what Pikmin said.
Well, there's two ways that I look at this song:
The person who is speaking is/was a best friend (or a bf/gf/spouse) who happens to be dead but will always be in your mind. (Although they could be alive too.) They realize that you had been alone without them all this time.
It could be an evil enemy who's taken over/trying to take over your mind. Or they're just threatening that they'll always be there in your mind. (Like the theme in the movie, "Cat's Eye" with the song "I'll Be Watching You". Or if you've recently seen that cartoon, "Teen Titans", when Slade was in Robin's mind, and no one else could see him except Robin, in which he was perceived as going crazy).
But I like to think of it as my best friend with theory #1 more. Although I can see what Pikmin said.