When relationships end in our life, even relationships that were difficult and conflicted, it makes us sad. Simple as that.
Accepting my feelings was a hard part of getting sober. I stayed away from them for so long by numbing myself. You owe it to yourself to allow yourself to feel. As much as it hurts, as much as it sucks.
What helped me was staying connected to people, which meant I had to allow myself to be vulnerable- another thing I'm not good at. But after a few years of riding this out over all the hills and valleys things have gotten so much better.
I am sorry for the loss of your marriage. I wish you all the best.