EDIT: I am doubly screwed because I signed up for the employee stock option loan program... and I'm not sure what the bank will want from me now that the stock price has tanked.
When a relationship ends, there is a loss, often a deep one. And because cognitive dissonance is hard, we automatically reinforce rather than balance that feeling of loss. So right now you're focusing on how this is terrible and a major negative in your life and how wonderful she was - catastrophizing the breakup rather than coping with it.
Try making a list of everything that you didn't like about her and the relationship. Also make a list of everything you don't like about the future potential of that relationship. Remind yourself of the things on these lists regularly. A key one to include: given that she ended things "abruptly" you likely feel abandoned. So let me ask you this: knowing what you know now about her, do you think she'd stay by your bedside when you're on your deathbed? However bad it is to be abandoned now, it's much worse to be abandoned when you're alone and scared.
https://www.scientificamerican.com/article/how-to-recover-fr...
But one day the the pain will end. And you will be able to look back without overwhelming feelings. What is important is that you will not do too much damage to yourself in the meantime.