For one you're not as alone as you may think. Things can and will change, you just don't want to feel this way. Concentrate on what has gone well, not the negatives. We're very good at putting ourselves down. Emotions are not permanent, and situations can and will change. Again.. concentrate on the positives, nothing is set in stone and any mistakes made do not define who you are.
Hope you're in a better head space soon! Take care