I understand. I struggle with anxiety and have for a long time. I was taking a prescription medication and it worked well. When I weaned off of the medication I was suggested to try several different vitamin type regimes and they have been successful. This is not medical advice and without knowing your medical history, it would not be ethical for me to advise you on what to take, but I will send you links that I have found helpful and you can decide what is okay for you. On the third link, skip down to where it discusses the vitamins. You will know what is best for you.
As far as part of accepting what is going on in your personal life right now, I can understand being upset. It is not easy to watch with "regrets" as someone whom you care for is moving on in another phase of life. However, without sounding calloused, is it possible to process from the "end" or thinking about your long term goals, that are personal for you. Maybe not necessarily about her. Maybe try focusing more on the health of the relationship that you want. It sounds like she feels that working things out with you is not possible at this time, but it does not mean that she will always have this mindset. My encouragement is that you do continue working on your personal counseling or finding the regimen to combat the anxiety you are experiencing. You have to be healthy before you can have a healthy relationship. It seems that you are taking a great deal of ownership and I respect you for that, but don't get stuck in the "bargaining" stage of the grief cycle right now. Any time that you go through a loss or a breakup there is the presence of the grief cycle. Different phases of the loss will be evident thorough different phases. You most likely experience, disbelief, denial, anger, "bargaining", depression, and acceptance. These do not necessarily go in that order, but you experience them at different times. We have been taught that grief comes in waves, but for me it is more like walking along the beach-- If you have ever walked on the beach you recognize that the sand and tide are often different depending on factors. No matter how dry the sand feels at the surface, if you dig your toes in a little deeper, you realize that it is still "wet." That is what it feels like when you have been hurt-- the pain is always there. So right now, it feels like you have been cut open and have a gaping wound, but this is part of your grief. You have this guilt that rules your life causing you to feel that you are completely to blame and she had this resentment toward you that you wish you could change, but (and I know you don't want to hear this) you can't make that decision for her. However, what you can do, is think back to the man that you are, the man you are created to be, the man that fathered those children, and be "that guy." What made her fall in love with you in the first place? Recreate that confidence, recreate that assertion, find that esteem and see what comes to you. You have to accept the relationship and the possibility that it was over and focus on how you are going to be stronger. You are stronger than this and you are hurting yourself by feeling that you need a sense of control-- control over others is an illusion. You only have control over your emotional reactivity and choices that follow. My encouragement is to try "stop thought" techniques, try focusing more on your worth and esteem, and think of the father that you want to be.
What is your feedback so far?