What do you think of this ?

You see i've been talking to this girl lately and the other day we went on a good date and made out, got a little closer to each other. But yesterday my friend invited me to a party and he talks to my girl too. The thing is, that he told her that I was going to the party with him and she text me saying how i was going to go with him. From a mans standpoint was it wrong for him to tell my girl that knowing how closer we're getting to each other ? I mean shes been acting different since and idk what to do. Plus I only went with my friend because i havent hanged out with him in a while and i didnt want to say no plus we didnt even end up partying. Am I overreacting ?