The Lights of Avendene by Isabel Murray

Jack. The duke. An alpha in love with two very different men—his prickly young alpha servant, and the shy omega childhood friend he vowed to stay away from…but just married.

Beckett. The servant. An alpha from the slums made good. Stupid enough to go and fall in love with a duke. Mad about it. Now Jack’s up and married an omega. Mad about that, too.
Arden. The omega. Betrayed by his brother on their father’s death, whisked to safety by the only man he’s ever loved, and apparently not too old and withered to go into heat for the first time.
Unfortunately, his new husband’s stuck in town and there’s only one suitable alpha at Avendene who can help: Beckett.
The servant who loves Jack, and hates Arden.
How can a beginning this bad possibly end in happily ever after?

The Lights of Avendene is an MMM omegaverse fantasy romance set in a Georgian/Regency-esque world, with an alpha couple, the inexperienced omega who ends up between them, a lot of hurt feelings, a hint of danger, and a love worth fighting for.