Whenever I try to do something to my mod in the GECK, it immediatly crashes. Trying to save it, replacing, adding new items, etc. This didnt start happenening untill i worked on the museum station (metrocenter07). After this started, i can load up any cell but that one, and when i play the mod it works but when i go to that station it crashes. Lucky for me i had a backup from two days ago so i loaded it up, did some work, even on that metro station again, only to have the exact same thing start happening. I got that backup again, deleted that metro but after a few hours of work it happened again. It repeated itself 3 times after. What could be wrong? I cant make any progress as i have to keep going back. Is this particular metro known for this? I really have no idea what could be wrong, and its frustrating to have to keep going back.

Some things that can be causing the CTD.

1. You retextured a furniture object that is in the cell using a texture set.
2. You disabled or deleted a vanilla game object that was in that cell.

If you remember what you did 'last' in that cell it would help determine the problem.

Well, now that i think about it, i did add a "null texture set" on the metro bench's cracks. Could that be the problem? It would be a huge relief to know it was something small like that.

I don't know what a "null texture set" is, but since its a furniture item, then yes, that would be the problem.
For furniture, you need to copy the NIF and edit it directly. Then you can load it into the GECK as a new furniture item and it will work.