navy boyfriend

my ex boyfriend of about a week is in the navy and hes about to go on deployments and hes always been scared that id move on from him while he was in a submarine but id always try to convince him that im completely his. well he broke up with me and even though he still loves me, he wont get back with me because he is scared ill move on and he doesnt want to put me through the stress of him being gone. but im so willing and ready as a girl to wait for him and love him while hes gone and when he comes back and be totally loyal. what can i do to convince him of that? what can i do to get him back? we both know we are in love and we have always been certain it was true love and we are meant to be and he always talked about marrying me..how could things change so fast.