Why has my ex gone bunny boiler?

Hi, I was with this guy for a few months and I was crazy about him, he dumped me out the blue 1 week after he has introduced me to all his friends, everything was great h seemed pretty smitten with me too, then BOOM! he just broke up with me the following week, its been 1 month since that now and Im seeing someone on the rebound, I changed y status on fb to 'in a relationship'. I had tried to stay friends with my ex but he was **** at staying in touch and cold with me so I washed my hands of him, but 2 days after I changed my fb status he rang, I never called back, then yday he messaged me on bbm, I was in the cinema so I didnt reply, he then messaged again (because you can see when someone has read your message and not replied on bbm) saying 'ok I wont bother you again take care x' then I tried to reply when I got out the cinema and he had deleted me as a bbm contact, whats up with him? why did he break up with me for no REAL reason? and why the sudden interest again? does he still have feelings for me? or is it something else? help!