This is the curse of being a zoo. Our partners usually have a much shorter lifespan then us.
I still remember the very first mare I bought. The story of how we ended up with each other felt like destiny, and have so many fond memories of her and me wandering through the forest. When she passed away I never thought I'd have someone like that again.
Traveled the world for a while, came in contact with many different philosophies. And came across a beautiful passage in a Buddhist book. It compares our life to a waterfall. Before our life we are part of a river. When we are born our journey down the waterfall begins, as individual droplets. But in the end we all end back up at the bottom, together again as the river of life continues.
I don't know why, but this passage brought me great comfort.
Since then I found a new partner, not to replace my first mare, but to add to my circle of love. As well as my dogs and all the other critters running around here. I know I will probably outlast them all, be heartbroken, but know we will join up again further down the river.
I know it sounds a bit hippy dippy, but that is how I cope with lost lovers.
Hope it helps you out a bit.