Should I be mad at my by?

My boyfriend was a baseball player for our school and had been his whole life. One day I get a text from him saying he was staying after school with his guy friends and these two girls to play tennis. These girls are thin and popular and have lots of money and are on the tennis team. He doesn't even talk to these girls so it was surprising he was playing tennis with them (his friend asked him to play tennis and he said yes and the girls just so happened to be at the courts). I got mad and we had a fight. I trust my boyfriend and know he would never do anything with another girl and I was being stupid but it still made me mad. 2 weeks later he quits the baseball team cause of some problems with the team and he is now on the tennis team. Ironic. I'm being ridiculous and don't need to be mad but I can't help it.