Wife has strong feelings for her ex

My wife and I have been married for 22 years and have a good, happy relationship with 2 children (12 and 10). She did, however, have a very intense relationship with a previous boyfriend before getting together with me. They are also part of a larger group of friends. When we were first married I had no problem with them seeing each other on occasion, both in their group of friends and on their own for drinks and/or meal out. I felt very secure in our love and our relationship and it didn't bother me as I'm not one to be possessive. By the time we'd been married for about 8 years, however, and before we had children, things did "spill over the line" with them, and it turned out that a few of their evenings together became very intimate (not sex, but kissing, etc) and it was clear that they were becoming romantically close again. They then stopped immediately at that time, and my wife felt terrible about all of it. We worked through it, but while she loves me and wants to be with me, she - to this day - continues to feel a sort of connection to him. She doesn't necessarily want to be with him ever, but she is attracted to him and worries about him (he has had many other girlfriends and one steady one for a while now, but he has trouble with committment and may never marry - perhaps all of this would be easier if he would!). I find all of this extremely difficult, and where I once felt trusting and non-possessive I now feel basically the opposite when it comes to this man and my wife. This is difficult because she does still want to be friends with him and they do see each other in their group of friends 2-3 times a year. But I find those times very difficult, and just don't know what we can do about it. We do talk about it, and its not that I think anything will necessarily happen now between them, but I just don't like the notion of any intimacy whatsoever between them now. And I just feel so sad that she has these underlying feelings for someone else. She says that it's only a small fraction of what she feels for me, but that its there. How do I get over these feelings? Or should I? Thanks, Artief