Looking for advice and not been on the site before so bear with me. I have been divorced for several years now, reasonably amicably, and my 2 children (13 and 10) split their time between me and their dad. I am with a long term partner, and the kids have always coped well with the situation. Soon after we split, when I met my new partner, my ex also spent a couple of years with a girlfriend. She was lovely, great with the kids and I did not feel threatened by her in any way. I wasn't her friend exactly, but viewed her as a safe pair of hands, if you like.
Now, I have recently found out my ex has been having an affair with a married woman (with 2 kids) who happens to be someone he had an affair with before we were married. We had been together 4 years, and they had a fling which I found out about and was devastated about. Then they went their separate ways and we were married the following year.
So now she is back on the scene, and I can't bear the thought of her getting to know my children. It has brought up such a lot of negative feelings for me about the past, and how betrayed I felt. I want my ex to be happy, I really do, just not with her. I realise I have no power in this situation, but I need advice on how to handle it. If you can follow the above (I know it's complicated!) then let me know your thoughts.