It means
You are pretty therefore I.....
Literally translated 'because you exist'. Figuratively it can mean 'because you're here/there', 'because you're with me' and such.
Kimi ga Iru Kara was created on 2009-12-02.
'Kimi mo ai shite iru.'
Kimi ga Iru Dake de was created on 1992-05-04.
It depends whether you want the English theme song or the Japanese. The English theme song is "My Hands" By Leona Lewis. The Japanese theme song is called Kimi Ga Iru Kara. I don't know the name of the Japanese singer.
Kimi no Tame ni Boku ga Iru was created on 2001-04-18.
It is simply called 'ft', presumably short for Fairy Tail.
Try www.onemaga.com
'Because [I] believe [something]'
My nihon is scratchy, but it's better then nothing I guess. It means something along the lines of "because you're by my side (/with me)" depending on the setting.
anata WA kangei + your welcome not so sure about the "suite iru" part
You may use the verb 'kusatte iru' to mean 'rotten.'
'Iru' can have several meanings, among them "to exist" and "to need."