Although they are no longer a couple, they're still family in a way - you wouldn't expect him to stop all contact with sisters, female cousins etc would you? I know it's different in that they've had a physical relationship, but that's all over now and they still have a lot of history together. If he was seeing her behind your back then I could see your point for worrying but he's being perfectly open with you about it. If you make a huge fuss about it then he's more likely to start hiding it from you so as not to upset you, and that can only lead to problems as he'll feel he has to keep secrets from you, leading to a less than honest relationship. Lighten up and accept it for what it is - a friendship. I lost my best friend of 20 years because his new wife didn't like him having a female friend. We've not spoken for over 2 years and I miss him every day, and I can only imagine that he may come to resent her for making him give up such an old friendship for her when she had no reason to worry or be suspicous.