Will a starter slowly go bad or is it instant Motor started turning over slower and slower over a couple of days and I don't know if its the starter or battery?

yes that's exactly what happens, the starter can get slower and slower over a couple days and then it won't start at all. you won't be able to "jump start" battery either. starter must be replaced..if u can find a used or rebuilt one, they're jst as good. new starter approx. $90-$130. used around $40