>>23319140
>But... it is a thing in the actual shows.
No, they are not romantic partners. It only appears that way, but there's no relationship in either case.

While there was something between Athrun and Cagalli at the end of the first series, that was curtailed by her "responsibilities" as queen of Orb and is not coming back. And even if Lunamaria and Shinn have feelings for each other, they aren't a couple.