If you find that the feelings and reactions are pervasive try dedicating time each day say ten to twenty minutes to reflect on and experience the loss. Set it aside and if the feelings are triggered through the day take a slow deep breath and allow the feeling to pass like clouds in front of a mountain. This can help you focus on your work or other important things that you need to do.
Choose to let go of bitterness and focus on the life you want to create going forward. If this is hard pick a physical representation i.e. a pebble for each bitter thought. Feel how heavy that container of pebbles is. Do you really want to carry that around forever? Gradually lay down those pebbles one at a time over the next while until you are free of the weight of them.
Forgive. Forgive your self, learn from your mistakes and understand your part in what lead to the demise of the relationship. Forgive your ex partner. This does not mean you are saying the things they did were OK but that you don't want to carry rage, bitterness contempt or resentment moving forward. They were not perfect that is for sure. They are indeed human however. As are you.
Don't dwell on how your partner’s life is unfolding. Take your energy back and put yourself five years out. If you were to have lived the life you wanted in those five years. What would it have looked like? Sounded like? Felt like? Contained? What experiences would be there? What would it have felt like?
Take care of yourself a lot of energy is required to deal with the physical demands of change and the emotional losses not to mention supporting other family members who have been effected. Some studies have said divorce is harder then death because of the support that is there for widows and widowers. I don't know if that is true but I do know it helps to have someone you trust that you can talk to.
Don't put your kids in the idle or anyone else for that matter. Your relationship with your ex was up to you and your partner no one else. The feelings you have are also between the two of you.
Accept differences in parenting besides that may have one of the reasons you have separated! Don't expect your ex partner to be any different then they were while you were married. Otherwise well you might still be together right?