[I admit I haven't read all the responses]

You've heard the adage I'm sure 'you want what you cannot have.' Is it perhaps the experience of the persuit that is the attraction?

If you really do love this woman - which is wonderful - patience is golden. There are proactive things you can do too. Have you had a sit down yet and discussed her mental health challenges? What about discussing your own thoughts and dreams? Showing interest in her will go far. Include her in your life and she may include you in hers, ex. I'm going to such in such, do you want to come along? Be careful though that you stop short of her looking at you as merely a confidant. Of course, there is always honesty. Ask her out.