My boyfriend made out with his best mate?

You should ask your boyfriend first about what you saw, maybe his friend was mocking him about you kissing your boyfriend bye. You did say Calvin likes to make fun of you. John was probably trying to shut him up. Alternatively, they may actually be jackasses. The only way you can find out is to talk to John directly! If you can't talk to him about things, then maybe you should reconsider being with him.