My bf is txting a coworker

So this evening i went to meet up my bf at olive garden when he took his phone out i saw a text from a girl named Maddy i askd him who it was which i know cuz i used to work with them for a while the txt read something like he had asked her what she was doing how was she etc. it was q long txt too. So after we finished eating i told him to just go home & txt her imstead he actually went to my house & told me that he had been texting her just about her dog i asked him to see his txt he had deleted them & i saw he has a pic of her on her contact & her birthday he said he didnt wanna tell me about her because he knows how i would go crazy on him. Am i wrong for getting mad cuz he doesnt see that by him deleting text say a lot or is he right he did that so i wouldnt get mad i want him to understand how i feel but he just doesnt