I need to end it but dont know how?

The Guy I'm with is very clingy... his birthday is July 7 and I don't wanna be with him anymore. How do I break It off. He's telling me all this juicy stuff like I have his heart and he loves me and isn't going anywhere. I'm 16. I wanna be single! I'm going to the beach And he wants to surprise me and come down there on my birthday which is the 12th. How do I end this quickly! I wanna do it nicely.