Silver by Wendy Rathbone

In a beta-ruled world where betas are sterile, the breeding of alphas and omegas is strictly controlled.
Silver lives in the Hall of Alphas, a fancy prison where alphas, considered dangerous by society’s standards, live out their sad lives while donating weekly quotas of semen to the world’s breeding programs via milking machines.
Tobin, a sensitive beta, works as a fluffer, someone who helps keep alphas with various sexual dysfunctions aroused for the milking machines so they can properly knot and meet their quotas.
Normally, omega heat scents piped into milking rooms are enough to send an alpha into rut, but when Silver loses his sense of smell and can’t knot, he is sent to the infirmary where he becomes Tobin’s responsibility.
A waaay more than professional relationship ensues.