Am I overreacting?

I recently found out that my boyfriend was talking to another girl which was my good friend behind my back. My boyfriend is very friendly to girl and doesn’t really set boundaries. It told me he is really trying to change and I see it he does not talk to the girls no more. But ever since that happened I’m just so scared I’m wasting my time with him. We spend a lot of time together but I don’t know he doesn’t respond fast, and every time we not talking I’m feel like he cheating. I just want to know am I over reacting? I’m a senior and it’s about to be the time for college we talked about it and we are trying to stay close. But I don’t want to waste all this time.

Am I overreacting?