Like, the PC isn't hooking up with anyone but you can pair up other characters to greater or lesser effect depending on how compatible they actually are
It would be an absolutely ridiculous amount of contingency dialog but "ridiculous amounts of contingency dialog" is basically my CV so
There's the fear of having to do exhaustive scenarios for every potential pairing or polycule, but thinking about it from a narrative standpoint:
Within a limited frame of time, it's not true that everybody could be with anyone else in the group. Although preferences change over time, nobody is everybody's type. Attraction is complex, but it can be influenced by environments and events.
Lynchpin moments can change the way someone sees someone else. I'm thinking transparent consequences to your situational choices, like Ladykiller in a Bind did. If you have an opportunity to push two characters closer, the game lets you know. All shit that I can mock up in twine without much trouble hm hm hmmm