Confused😕

My boyfriend and I have been dating for 8 months. Everything is good in our relationship for the most part. The only thing that bothers me is that he texts other girls. I've argued with a girl before and he stopped texting her. I've asked him to not text anyone else. He says he have been talking to them long before me and that I shouldn't be so worried. This conversation came up again with us yesterday. When he said some girl was jealous that we were together. I asked "Well why would you still text her? Knowing she doesn't like us being together?" Am I overreacting? 😕