Ok I think I get you now, though I think there's something that's confused me a little.
Cath and Gabby having a specific throuple implies to me there's something of a "solar system" kind of harem, where all the romanceable people orbit around the MC but are all their own planets fairly separate from each other (except in cases like Cath and Gabby who are together but separate from the other LIs). Otherwise it would seem that the size of any CathxGabby relationship with the MC would increase with the size of the harem, cause all those in the harem would be in something of a poly relationship with each other.
I can imagine that in the latter case none of the romantic interests could be feasibly missed or not pursued since the story's about the harem and the harem is interconnected, while the former would seem to suggest some people who could join might or might not necessarily do so since while there's a harem each love interest has a relationship that's fairly singularly focused on them and MC.
Not that any of that is necessary or anything! If the story always involves forming relationships with all LIs then that's all good and just how it be
. But the alternate possible interpretations have left me still somewhat unsure on whether you're building a harem of all, or pursuing a harem of some based on choices you take, paths you follow, etc., that can become a harem of all depending on how you play.