I have not had time to read the thread through but want to post.
The relationship is not a done deal but the one thing that is more important than that is you. You must put your own physical and mental well being first. When you are well the relationship issues will resolve themselves one way or another and you will be fine.
Its very difficult to hold a relationship together when depression is involved, I have been there. IMO the best thing you can do (but also one of the hardest) is to do exactly as she says and just date each other and have fun.
She's still with you so you have a chance to change her mind I'm sure she wants everything to be good.
You really need to try to live in the moment and stop yourself from thinking about past issues and future scenarios. You can do nothing about either now. This type of thinking can pull you further into depression.
Its the cycle, you become depressed and feel bad, your brain tries to work out why and how to fix it thinking about being depressed and causes more depression. If this was easy to stop then it would be easy to fix. You can insert any problems causing depression here.
Have a look at how mindfulness can help you in depression, this will help you to stop feeling bad in the short term. Try to just get through one moment at a time and the hours and days will take care of themselves.
As said by someone, setting short term goals and rewards are a good way to go and above all do not give yourself a hard time about anything, even if you think you should. This is counter productive for your mental health - dont do it.
If you crash the car, break your bike, stub your toe, annoy your loved ones etc - learn from it and just move on, put it in the past.
Find lots of little things that are good and live for them, there are ways though.