Having friends who used to be lovers is actually quite common, and nothing to be concerned with as long as she understands that the friendship must be open for both of you. Trust is a very big issue in any relationship, and the fact that you trust her means that you're relationship is on the right track.
You will want to sit down and go over anything that bothers you. Keep in mind communication is serious. Letting her know how you feel and what you are concerned with with help her understand how she needs to handle this relationship.
You may want to ask her if this can be a friendship for you as well....thus allowing you to be a part of the friendship. Since you are a couple while you may not share all the same friends you will want to be on basic terms with her friends as well as she with yours.
The biggest thing, is if something bothers you about the friendship then talk with her about it. Let her know what bothered you and how you felt. Though try to keep in mind most often these friendships tend to run there course. While she may feel indebted to him for friendship eventually overtime these friendships tend to die out. By being understanding and accepting of her needs you will in turn strengthen your own relationship with her.
I wish you the best,