Why does drinking decaf tea make me pee more? is it good?

Depends: Its a matter of volume- if you drink a bunch of tea, you will pee more with or without Caffeine. Keeping well flushed is a good thing as long as you are not getting too dehydrated. If you dump a lot of sugar in your tea, that is the sugar drawing more water out of your system that makes you pee more, and makes you more dehydrated. Watch the sugar and sweeteners, should help things