If you are using the same Gmail account this data is stored in the Google servers and you can locate what applications are and have been installed via the Play Store or https://play.google.com/store.
At the Google Play store there is a menu, 'my Android apps.' this shows all the applications that you have installed, but you have to login for that, so your friend must be knowing your password also. Change your password.
ok..thnx for the posts.
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