Best Answer - Chosen by Voting
"If one day you discover a cafe called 'Tea Amo' in Gulangyu Islet of Amoy, that (one) must belong to me, for I would spend my rest of life waiting for you."
"Se um dia você descobrir um café chamado 'Tea Amo' na ilha de Gulangyu, em Amoy, este deverá pertencer a mim, pois eu gastaria o resto da minha vida esperando por você."
I'm not sure if you wanted to say "I love You" or if you made a pun with English "tea" and "te amo" to create the "Tea Amo" name for a cafe. So I kept "Tea Amo".
You don't have to specifically refer as "ilhota" in this case as you're calling a place and not a geological formation, so "ilha" will do it.
You might also want to say "um café ... na ilha de Gulangyu, em Amoy" or "um café ... em Amoy, na ilha de Gulangyu", since it seems you have to mention Amoy to better refer to the island.
The conjunction "pois" sounds better then "porque" in that sentence as "porque" is closer to "because" and "pois" is closer to that specific meaning of "for"/"since".
In the case of "porque" it also never uses the article "o" in the middle, but there are some annoying writing rules regarding it, that don't change anything in how it's said but somebody made it complicated to write for some reason:
In the sentence your explaining something: "because"/"since" writes "porque".
In the sentence you're asking the reason/cause for something: "why" writes "por que" and "why?" writes "por quê?"
In the sentence you're asking the reason for something: "reason" writes "porquê".
But all sound the same, only writing has this problem, so don't worry much about it and try to avoid the last case using "razão" instead.
