It sounds as though your friend has somehow linked the character to a different ID. If you linked your Habbo account to Facebook and when you go to your Facebook account you can no longer log in, it's mostly likely linked elsewhere. If however you are trying to log in to that Habbo character directly via the Habbo site (i.e. using the email/password boxes instead of the 'Login with Facebook' link) then you won't be able to access the character as it technically has no Habbo created username/password.

If you use https://help.habbo.com/home and explain that you have ID problems and can't find your Habbo character now, they'll be able to sort it out for you.

As has been said above, it is a really bad idea to share your accounts with friends. YOU may trust your friend, but you have no idea who else your friend is trusting or even if the computers they use are secure. If you do share your passwords you will always encounter problems