People don't look at the death of a marriage the same way that they do a death of a person. In today's society, divorce isn't looked at twice. It's become the norm from what it was back 20+ years ago.
No matter if it's a death of a marriage or the death of a person, we still grieve and the grief can take years to work through and we bounce back and forth through the stages for quite some time before we finally settle down.
Closure for me was accepting that I did everything humanly possible to save the relationship w/o getting bitter and vindictive towards him. I can honestly say that I gave my xh the best 25 years of his life because he had the opportunity to do many exciting and wonderful things over the years that we were married. He lived a far better lifestyle than the one he came from during those 25 years.
Closure is different for everyone...you will need to determine what closure looks like for you.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.