In most divorces, and indeed in most relationship breakups, there is a person who has chosen to leave the relationship and a person who is being left. A key difference between the person who is leaving and the person who is being left is that the person who has made the choice to leave has had all the time they needed to come to that decision. They have had time to reflect on the nature of the relationship, to grieve over the end of the relationship, and to start to adjust to a new life outside of the relationship.
On the other hand, the person who is being left is usually to some extent surprised. They might know that things were not going well, they might know the other person is upset, they might even suspect that the other person is thinking about ending the relationship, but when it actually happens it is still a surprise, at least in part because they did not know it was going to happen THEN – on that day, at that hour, in that way. They also did not get to participate in the final decision – the first person to decide has made the decision for both. This means that the person being left has not had the same opportunity to contemplate, to grieve, to decide, and to adjust.
For the person who done the leaving, it is important to remember that other person, the one who is being left, will need time. They are just beginning the process you have been going through for some time. It will take time to adjust to the end of the relationship, and it will be even more difficult because they were not able to participate in the decision – it was to a degree forced upon them. Getting to the point where details of the breakup (how to divide property, what to do about children, etc.) can be discussed calmly and thoughtfully will require patience.
For the person who has been left, it is important to realize that the person who did the leaving is not heartless just because they do not seem to be in the same amount of pain as you, they have just had more time to deal with the pain and adjust to the idea of the end of the relationship. It is OK to let the other person know that you are going to need some time to catch up. By taking the time to grieve and adjust, you increase the odds that you can find the best solutions to the breakup issues rather than simply striking back in ways that may meet your immediate emotional needs but are detrimental to your long term goals – such as being able to co-parent effectively.