Jose Marti cattelya - black spots and casing, drooping

[sea view]

Hi
I am a total beginner, and I seem to be killing my first orchid - a Jose Marti Cattleya.
It has black spots on its leaves. The casing on one of the new shoots has turned black, and the whole shoot has dropped.
Another shoot has drooped and seems to be rotting.
I have been watering once a week. It sits a bright room which gets morning sun, but doesn't get much direct sunlight. I live in the sub-tropics so we have comparatively high humidity (between 60 and 90%).
Please help me rescue this poor beauty! It is too much or too little water? Not enough light?
Any advice will really be appreciated!