Recently my lens cover hasnt been activating my camera app. I have to start the camera app via shortcut or shutter button.

What did I break?

Maybe something wrong with the sensor of the camera.
Read this thread, maybe useful

If you take the back cover off, you should see two rectangles, one black and one white, on the camera door.
These seem to be positioned over a little LED/photosensor combination - You should check to make sure there is no dirt or anything covering those.

Check the output of dmesg in terminal to see if the shutter is being detected or not. I have a similar problem and it seems to be an app locking audio so the camera app can't open.

Same here seems to be related to fCamera install.

Mine wasn't working either, although most of the time I only wanted to use flashlight so that was fine... although i've recently replaced the little magnet on the back stand, and why I was there i gave it a good old clean...

Since then the camera app opens every time i open lens... however flash light (and gsm/3g button in status menu) has gone!

Without the magnet on the back cover, the phone ignoes the position of the camera door.

So I read the other forum, and I noticed my magnet under the kick stand is gone. The question is can i replace that with any kind of magnet?

from what imve seen on other threads her, pretty much yeah. been a few story's/pics of people cutting up and gluing on fridge magnets etc.

My fault, I think Im confused on what the back sensor is and the lens sensor is. i guess there is a sensor for the whole back cover because my memory card is not working. Where is this back cover sensor?