OP, I had some CBT a few years ago and something I learned then has stuck with me. It might be useful to you too.
I used to dwell on problems. Go over and over them in my mind, work out different ways I should have dealt with them... I could take something minor and spend years on it, literally years.
By doing that I was making my problems bigger, not smaller. By giving them all that time and attention and space in my head, I was making things worse for myself.
I have learned, over the years, to stop doing that.
Instead I think about something; work out what the best thing to do is; and then I do the thing, and stop thinking about the problem.
It's made things much easier.
If you can, don't let this occupy your mind all the time.
Remind yourself each time you think of it that you've done nothing wrong and are not to blame for anything, then consciously think of something else. Work out how you're going to move forward, then think of something else. Your studies are an obvious one.
I hope this helps.