This song is pretty simple.
The guy [presumably] loves this person. Obsesses over them. He is jealous and in awe of them as they are so special. He wants their approval and has a really low sense of self-worth. He doesn't feel he belongs because of this.
He eventually gets really obsessive and controlling over this person, and they leave.
There is a possibility the person loves him back [if he was really in love with them in the first place - may have just been infatuated], but he has such a low self-esteem that he can't see it.