[TOMT] Girl can see some supernatural creature

So I read this book like 5 years ago when I was in middle school so I don’t really remember it well. What I DO remember is that it was about a girl in high-school and she somehow finds out that she can see some sort of supernatural creature( it was either a ghost or demon or something of the sort). A boy(I think he went to her school) was that creature and would follow her around in his car and bother her. At one point in the book the girl goes to a party and the boy(being invisible) pushes her out of a window and into a pool or hot tub. The book was very detailed and I want to reread it so badly! Please help!