If it bothers you then you should talk to him and tell him how you feel about it. He has had feelings for her before and they can reemerge if they talk and spend enough time together. Tell him to cut off all ties with her, it's not that hard of a task to understand. If the shoe was on the other foot I'm almost certain he would want you to do the same. All will be well if you bring it to his attention and do what you must in order to avoid anything that an damage the relationship you two have.
