Find Me by A.M. Arthur

Layne Higgs grew up with a clear plan for his future: find his bondmate, mate during heat, and raise a family with the same love and devotion his parents showered on him. Until two years ago, he never anticipated that future would be with his best friend-now-boyfriend Peyton, and Layne has never been happier. Then an unexpected, impossible pregnancy obliterates everything Layne knows about himself as an omega.
Peyton Tovey has lived his entire life on borrowed time and that time is running out. With a baby on the way, Peyton agrees to participate in a risky gene therapy trial to save his life and give him the future he wants with Layne and their son. But the cost of the trial is more than anyone anticipates, and to have their happy future, Peyton and Layne will both have to find their way back to each other—or lose everything.