You seem to be going through a tough time. Focusing on those things which didn't work out for you and the negative meaning that you draw out of it will definitely make you feel more negative. Thinking about it repeatedly is not going to be of any help unless you are looking for clarity, what went wrong, why did it happen the way it did, what was your role in the whole thing, and what you could have done differently etc.
Next Steps
Please see a counselling psychologist who can guide you to make sense of the event without you feeling victimized, empower you to feel in control and recover from the trauma.
Health Tips
Turn your focus on positive things that are happening around you, distract yourself purposefully so that you can disengage yourself from overthinking. Find what is meaningful and purposeful in your life. This will give you hope and direction.