Why Du shouldnt go out with your ex

Well i was going out with my ex yesturday then he told this girl that she likes him that he going to brake up with me and i felt like a complet idoit because i was the last one to know about and he plays football and i play Vooley ball and he told me that he stills likes me he just need to think then he saw his other ex and he like i talk to Du tomrrow and just left running after her and im like WTF then my freind told me that he was playing with my enmotions and didnt really wanting to go out but he called me yesturday saying a hole buch of lovedove things so idk no Mehr what wiil happened tomrrow