How do I stop ruminating my entire relationship with a covert narcissist?

Title: How do I stop ruminating about my relationship when I keep uncovering new things about it?

I’m 22F and recently went through a breakup from a 4-year relationship (he discarded me, blocked me everywhere). I’m also a final-year med student going through my final exams, so the timing is honestly terrible. My biggest issue right now is constant rumination — my brain keeps replaying the relationship and analyzing everything.

Some important context:

The first month of our relationship: Within the first month, he went to a friend’s college, got another girl’s number, and kept talking to her for months. When I eventually confronted him, he said it was “nothing.” That incident kept resurfacing in arguments over the years because it never really felt resolved. It was the first big incident that created lots and lots of trust issues for me.

Avoidance of confrontation: Whenever difficult topics came up, he would usually minimize them, deflect, or just avoid the conversation entirely. Over time this made me feel like I was the “difficult” or “angry” one because I kept bringing things up.

Things I discovered toward the end: Near the end of the relationship I found things that made me question a lot of what he had told me — deleted chats, other accounts, and signs that he may have been talking to multiple people. It started to feel like he had a kind of double life that I didn’t fully know about. He went to this new college for doing post graduation where he pretended to be single or broken up idk....and was living a life without me in it...he created a separate ig acc, snapchat, blocked me from it...lied to me when he wanted to be with those new grp of friends and girls and when i figured it out he gaslighted me till the end.

When I confronted him about everything, instead of trying to clarify or prove anything, he basically chose to exit the relationship. He also seems to have moved on very quickly and may already be involved with someone new at his new college.

Now my mind keeps doing this thing where it replays the entire relationship from the beginning — especially the first month and all the red flags I ignored. It’s like my brain is trying to reconstruct the truth about everything. He legit lovebombed me for an entirr year...I was an insecure vulnerable kid so i thought he was genuinely interested in me and also he was friends with me too so yeah.

The problem is that I have extremely important exams right now and this rumination gets really loud whenever I try to study.

For anyone who has been through something similar:

• How do you stop your brain from replaying the relationship over and over?
• How do you deal with the feeling that you might never know the full truth?
• How do you focus on important responsibilities while processing a breakup?

Any advice would really help.