You've not let anyone down. Sometimes we do crash, that's a fact and it's ok if we still keep trying.
I don't know about your history and don't quite know what to say to help, but I can't walk away after reading your post. When do you next see your therapist, perhaps they can offer some support.

Please take care and if you need to speak to anyone (just chat... to keep your mind of things/her for a little while) feel free to message me