After you break up with someone it is natural to want to move on. Some people move on quickly instead of dealing with emotional issues. This is not a good idea for a lot of reasons. First of all, to be able to REALLY move on, there needs to be closure. You need time to heal. Even after the divorce is final, you need time to accept the past, put the focus on yourself and figure out what it is you desire in a partner. If your divorce is messy and emotionally exhausting, what kind of start is that for a new relationship? You need to be able to devote your attention to the divorce to make sure that you are making the best decisions since what is stated in the final decree will affect your future. Also keep in mind that dating during the divorce could possibly bring up custody and parenting issues. It is best to wait until you are able to put the marriage behind you before you start dating.
Letting go is difficult. Your spouse is out on a date and you are left wondering "How could they move on so easily? My spouse is treating his new partner better than he ever treated me! I still love my spouse! How can I move on?" Now is the time for you to get control of your emotions and let it go! This isn't easy, but you need to focus your energies on your children and yourself. Remember that your spouse is going to do what they want to do and you have no control over them.