How come my free ram keeps getting less and less?
Do not worry about your RAM being full as in a Linux OS it is not a bad thing. The system tries to fill up your RAM as you open applications and whenever you open an App again it is loaded from the RAM which takes fewer resources then loading the App from scratch. Letting an App stay in RAM does not take a lot of resources and the system is smart enough to only keep the most frequently used Apps in RAM.

So unless you are experiencing severe performance issues you do not have to worry about the RAM being full.