Talking to another girl

Hi ladies! Any thoughts on your guy constantly talking to another girl like everyday? He usually starts the conversation and seems that he enjoys talking to her. I told him that I was not happy about it. He said it was nothing and I shouldn't be jealous about it. I told him that its not bad to talk to other girl friends but you don't have to talk to her everyday all day *thankfully the girl is pretty busy with her studies*. He said he doesn't get why he should stop talking to her. So we agreed to cool off for a month and the day after that he was still talking to her. Am I over reacting and over thinking? :(