Get cheated by gf💔 it still haunts me

I'm a Bengali from kolkata a simple introvert nerd type boy from beginning I've a healthy relationship with my gf for 2 years but she cheated on me during last 3 months of relationship i felt shattered it's also affected my boards it was 7 days before then I find out.i do extremely bad in boards.I got 83% only My gf was 3 year 4 month senior than me and always spent the bill by her own everytime she cared for me she taught me english from 0,but idk what happened to her why she cheated she even asked me for 2nd chance but idk why can't I give her even though I want her to give i moved on but I've regret to choose her as 1st😭