Unfortunately your kind nature has been used here.
So pleased to read of your bravery to find a room.
It sounds as if you have been very stuck for a long time.
Before you leave, this would be an excellent time to do a clear out.
Get rid of old clothes and stuff you don't need.
So when you are leaving packing up will be easier for you.
Gather together any important paperwork or documents. Could you leave them in a locker at work so they are safe, before you tell her.
Getting organised before you leave, having gone through your belongings, will really help you move quicker, more efficiently.
Best not to be dragged into a long breakup conversation.
Keeping it simple to "this is just not working for me, it hasn't been for a long time, no one is to blame, just best that I move out now".
Keep practicing that, nice and simple so that you know it off by heart and can stick to it.
Hopefully you will be able to start saving, looking to your future, improving your job prospects, qualifications and move forward in your life.