Pease help me!?

OK, my ex boyfriend who i have been broken up with for like 5 months has beeen commming onto me for the last few days at school, he just broke up with his girl friend and i jus broke up with my boyfrend, lt night he txted me " i need a new girlfriend" then we stared talking to me really sweet and i told him i really wanted to go back out with him then he goes "well lindsey asked me out so im gonna go out with her" what should i do , i feel lied to decieved i cant sleep or eat i need help what should i do about him ?