From Thok, With Love by Susan Trombley

Can a grieving widow find love again with an alien who’s more tree than human and whose touch is toxic?

Frannie
Still grieving for the husband I lost during the invasion of Earth, I signed up with the Human Outreach Alliance Network to become a bride in an arranged marriage with an alien. I don’t expect to find love in a match meant for political alliances, but I hope that leaving Earth behind for another world will free me from the heartache of my past.
The Valentine’s Day reveal of my future husband leaves me in shock and despair. My “match” is a Thokost—an eight-foot-tall behemoth of a tree-man with a toxic touch. I’ll need to undergo a series of experimental treatments to make me immune to his toxin.
To my surprise, the letters we exchange during the painful process reveal an unexpectedly sweet and thoughtful side to the four-armed, four-tailed, bark-skinned alien. My match to Zanthos may not be a disaster after all.
But on Thok, the rules require more sacrifices for us to be together. This time, I may not survive them.