This one is where the couple hook up but the seme meets his fated pair (I think?) http://www.mangago.me/read-manga/shounen_no_kyoukai/
And there was one (totally forget the name) but the uke was bit and raped by an Alpha but ended up getting together with his childhood friend who was a beta and they had a baby. I’ll look for the manga but at the moment I’m not sure of the name :/
http://www.mangago.me/read-manga/romantic_joutou/ The one where the omega ends up with his beta friend
http://www.mangago.me/read-manga/tadaima_okaeri/
Its got a sequel and its in the raws that seme meets fated person
Looking for omegaverse with “reverse mating?” where the pair mate but aren't fated but meet their fated partners? http://www.mangago.me/read-manga/okusama_ha_alpha/uu/okusama_ha_alpha-chapter-1/6/ Something like that described at the bottom