Husband Texting Female Co-worker...

Hi! So my husband occasionally texts (outside of work) a girl he works with about things not relating to work. She is older than him and he says that she reminds him of his sisters and doesn't think of her in any way. But she keeps texting him outside of work, and he keeps responding, and then he forgets to tell me when they have texted outside of work like I've asked him to. So I find all of their texts that look too friendly for a married man to be having with a single woman. Am I just being paranoid? I know I'm insecure but I know emotional affairs happen on accident all the time and that they can lead to physical ones...