
No! one mate is not enough!!! why should the Alphas have the advantage always? the Alphas can be with more than one partner while the Omega if he's bitten has to be with only one? i think it's time that Omegas have more than one partner though. Or the Alpha can reject the Omega even if it's the destined pair.

Oh I do know 1 manga like that,
http://www.mangago.zone/read-manga/romantic_joutou/mi/602cc50aa90f0303847b3cf8ca8744c9_chapter-1/

just found out another one similar
http://www.mangago.zone/read-manga/kurui_naku_no_wa_boku_no_ban/mf/c001/
I'm confused. It's hard.
Just tell we had an omega(A), alpha guy(B and C).
Say A guy fated with C guy, omega body attract and react.
The other side A like B guy, but the omega body didn't response.
C guy suggested to have threesome relationship.
Didn't 1 mate it's enough?