Always means you do something regularly. For example: I always brush my teeth, before going to bed. Forever means till the end of time. For example: I will love you forever (which means I will continue to love you till the end of time, for eternity etc.) sometimes they can be used in each others place. For example you can say: I will always love you but you cant say I will brush my teeth forever (because it means you will start brushing your teeth and continue doing it till the end of time, or till you die :) )