Husband talks to ex

So I just found out my husband has been talking to his ex everyday for about a month now. They dated 11 years ago in high school. They recently reconnected through Facebook. He says there is nothing going on but a friendship. But it bothers me so much and makes me feel pretty shity and insecure like there is something going on, we have 2 boys and a 3 month old baby. I hate feeling like this. She is married and lives across the country. I told him it makes feel very uncomfortable and I don’t want him talking to her. But he says I shouldn’t worry about it. How can I not worry about it? Am I wrong?