i think that Urahara was working with aizen in the begining but backed out once aizen got too far ran away and hid the hougyaku,or another thing maybe aizen was hoping to get urahara on his side ,so that si why he said these words to him,and maybe after that urahara joins aizen fro a while then leaves aizen after he hide the hougyaku and so,but this theory is pretty strong i posted a similar one on another thread
