Some possibilities :
His account is set to auto login, maybe using a "Remember me" feature. Try disabling that feature.
You may have a mail checker active set to periodicaly check his account. Any automatic mail checker need to log in to check if there is any new mail, and, usualy don't log out.
Deactivate any email notifier.
If that don't work, you can install another browser.
If you actualy use internet explorer, you should try Chrome, Firefox or Opera. If you search, you may find some others.
Using another browser, his session and yours are totaly isolated. If he's logged into anything, you can log in the same services from another browser at the same time without any interferences.
A hint to make your questions more readeable : Always add a space after any "." "," ":" and ";". Use proper capitalisation, personnal names and the first word of a sentance always have their first letter capitalised. Ellipsis "..." and any dot strings are to be used sparingly, if at all. Refrain from replacing words wit digits or single letters. It may be tolerable in a texto, but nowhere else.
Electro
July 2014