My boyfriend knows my email address ,i dont know his?

is there any way can i find out what my boyfriend email address or to see if hes chatting with different women on the computer . i dont like the idea , he having my stuff . and myself not having his , also he s on hee all the time day and night .thats his job ,selling ebay, also he has the hots for young women and cameron diaz and any one young ...please help