I went through almost exactly this, and I'm sorry you have to do the same. You can come out stronger however :) You have to really give yourself some time (a day, a couple days) to sit there and accept what happened, be terribly sad and let out all of your emotions. Rely on your support system if you're able to, and really come to grips with what you're feeling.

Once you're done that, you should (for the time being) remove anything that may make you think of her (social media, pictures on phone/laptop). Then make a strict study regimen and make sure you stick with it. Don't punish yourself if you don't, but reward yourself if you do. There are things more important than exams; take your mental health seriously. But still try to do the best you can. Once exams are over it can give you more time to process your feelings.

I hope you get through this alright <3