The term you should’ve probably used shouldn’t be cheated. She hasn’t cheated on you, but she has kind of filled the void but yet, for the amount of love she has for you, she couldn’t conceal this and had confessed this to you. I remember your earlier post and you mentioned she is a 20yr old girl, so she might be finding it difficult to manage these 2 at a same time.
You said you live at a place away from her, so it would be hard to spend her days alone and she must’ve merely chatted up with him a few times, thats it. If she had really cheated or even thought to cheat you, she would’ve done that long back and she wouldn’t have told you anything until you found out.
The options are pretty clear, if you love her and believe she loves you, accept her (I recall saying the same, the last time) no matter what and make sure you get to her by immediately finishing your studies or take small breaks and try visiting her and tell her in a comforting way to not talk to him, she will understand. If you don’t like to trust her and accept her again, leave her and go on.
I think she would get down with a little one-on-one time, so meet her and try to be close to her at times when you get time from your studies.