I need your opinions and advice.I really believe my fiance checks my comp./inter. activity on a daily basis..?

My fiance (of 18 months) has all of my pwords and user names, which I willingly gave to him.. He has gone into my e-mail and history numerous times without me knowing and for some reason suspected I was up to something.. which is really not true..He sometimes accuses me of going on to dating websites, yahoo personals, my space..etc..The funny thing is that I would never want to meet or date anyone on-line anyways...(I just don't think it's safe.) Some of these websites have personal profiles of me that I never even created. This scares me...Is somebody playing mind games with me..or what?? I am frustrated and confused as to how this issue in my/our lives will be resolved...if ever..