I can see a friend's Details on my app.

Please be aware that in our Terms of Service (Account 4.5) it states that "customers may not distribute, share, transfer or permit their account information, including passwords to be used or accessed by any third party." 

Trying to share logins is not possible, because the subscription is linked to the Apple ID or Google Play ID of the phone itself, so you risk being charged twice or being locked out of your account.

You both have paid for a subscription but are accidentally using the same account. You will need to create a new account via “Sign Up” for yourself, so you both have your own account. 

You will not need to pay again but if you are prompted to do so, please select the subscription duration you have paid for and click "RESTORE".