Unexpected Mate by Harper B. Cole

Carter didn’t believe in true mates… until he met Brand

One scent was all it took. There was one big problem… when he met Brand, he was at a prenatal visit with his mate, Aaron, for their first child. And Brand was Aaron’s doctor. Carter wasn’t going to let the pull he felt toward Brand ruin what he had with Aaron, though, and Brand kept silent, so he let it fade.
Six years later, a car crash changed Carter’s life
It tore Aaron from him and broke his little boy in ways they are still trying to heal two years later. Carter’s had two years of grieving, and he’s ready to see if Brand and fate will give him another chance.

Brand absolutely believes in true mates… and Carter isn’t his

When Carter approaches him, Brand has no idea what he’s talking about. Brand’s never experienced that lightning from the sky moment, the fireworks, the scent–but he wants it. He wants it all. And he’s not going to take anything less than everything, no matter how attractive Carter is.
If Carter can’t win Brand over the easy way, he’s determined to do it the old fashioned way: with lots of wooing. But unknown to them, Brand has come to the attention of a group that poses a danger to all shifters everywhere, and their problems are just beginning.