The best thing to do is go to a clinic and get checked out. I would say do not have sex until you are 100% sure it is safe and it is nothing bad. If he has a history of being unfaithful, it could have just been 1 time he decided to do something and it had a consequence. I do not know you or your boyfriend so I don't want you to think I am saying things to be mean, just being honest about what could be wrong. I hope this helps.
Thank you I'm just really nervous because we both got checked out around the same time.