HELP?!?!?!? THINK MY bF MIGHT BE GOING BACK TO HIS EX!!!?

me and this guy name michael that i have liked since september just got together, becuase he broke up with his girl friend ( that hes been going out with since september). We got together yesterday and know his girlfriend is going to write him a letter saying that she still loves him and all that stuff. and she is mad at me because i told her that i would never go out with him and call him an idoit because i tought he liked my friend chelsey. and ido call him and idoit because i tought he liked my friend Chelsey. but i am so affarid that hes going to dump me for her. and if he does my heart will be broken really bad and i will cry and cry and cry and cry.I just nedd some advice???