What is wrong with my ex? Please help?

omg this is very similar to what happened with me and my ex.. we were together a year,, we both loved each other talked of marriage etc went away for our year anniversary and it was amazing then 2 weeks later we have one little tiff cause i was insecure about him drinking and he went all distant and said he didnt love me anymore... he added his ex on facebook and went into town with this girl who i have always had problems with im betrayed.... he wants us to be mates soo i agreed cause we have to work together but he has completely changed hes dropped out of uni and goes clubbing most nights.. i know how you feel its horrible but there is nothing you can do until he sees sense.. you gotta try and move on go on dates with other guys.. act like your happy and in a few months time he will come running back... hopefully both our exs will see what a hug mistake they have made.. lets hope it wont be too late.