New idea i thought of. Becoming a third wheel to a couple or a married couple. Basically if a character is in a existing relationship with another, you can passively feed both of them and slowly gain both their trust, making them fat and immobile. You find one with another, you get two blobs >:).
There could also be couple personalities, like A Trusting/Untrusting Couple, a Feedee Couple, a Feeder Couple, a Athletic Couple, etc.
(it also introduces couples and existing relationships and marriages to feel more real, but I feel like its more of a QOL thing...)
((Edit: Oh and to clarify, I don't condone cheating, ntr is also something I ain't into, but having it as an option like health issues might make some people happy :/ ))