You need to confront him about it, ask him for an explanation behind his actions. But before that you will need to compose yourself and prepare well. He may accept it or deny it, or he may accept it and break up with you. You should be well prepared to handle the outcome. The best way is to investigate for yourself, have tangible evidence, and then you can confront him confidently and calmly. That way you will be able to know the truth.
uhhm u jus.need to get rid of him! if he is cgeatting on u than he does not really caer about u or how u feel so its time to just move on! u deserve better and u deserve some one that cam comit to u in the same way u comit to him!
If you are sure then it's time to get a backbone and break up with him. Now is the time to learn to stand up for yourself and not let someone treat you poorly. You are just dating - he is supposed to be on his best behavior.