Whats it mean when your thinking of a certain person an your stomach feels like !

alright so i had major feelings for this boy we recently broke up because he wanted to get back together with his ex.. its been a pretty bad break up i live with him an hes not even coming home and when he does he gets clothes an leaves without saying anything to me except when he leaves he says "be easy kid" anyways ill be sitting in the chair and look up at a photo of him an start thinking about him or ill be watching tv and think i hear the speakers in his car boomin as he pulls in but hes not there everytime i think about him i feel like my stomach is dropping.. what could this mean on my part also what could i do to help him not to hate me anymore an maybe work everything out with him if thats even possible.. your help on any of this would be greatly appreciated