Except that transfer partners aren't bonded-for-life. Every sime needs transfer (or a kill) every month, but it doesn't have to be one specific person. If s/he meets a gen whose selyn production rate exactly matches his/her usage rate, they can get locked in synch--but this is not a lifebonding as much as a physical addiction; the body's very very comfortable when someone who's an exact match shows up, and goes into distress if that person goes away. (Biologists insist there's no emotional elements at all except those caused by temporary adrenaline & endorphin rushes; romantics insist that matchmates are fated to be together. Politicians support whichever side has the most votes this year.)

Yep, a soulmate vs reproductive mate issue would get similar results. So would something where romance/emotional bonding was removed from biological reproduction (f'rex, if you could only reproduce with someone with the same blood type, and it took a long time to figure out why some couples had kids and others just didn't).

Ooh, I do like fandoms where the adult relationships aren't presumed to boil down to "every person has ONE IDEAL PARTNER who is their ultimate companion for all purposes." There's maybe room to discuss the difference between polyamory of various flavors vs relationships that aren't love/romance based but are common enough that society's created a great deal of structure for them. They'd almost have to be derived from biology to get that common; the closest you get without biology is the buddy-cop dynamic that isn't necessarily romantic.