What is this thing that popped lke a pimple in his mouth?

okay, so my boyfriend said he had this like,,, pimple thing in his mouth and he popped it and blood or something came out.|||Get to a doctor! It could be herpes!|||It was a pimple. Don%26#039;t worry so much.|||could be like a canker sore|||idk but go to a doc cause it sounds serious