I wish I could recommend another one. But I myself am not that well-oriented in the weight gain games. I played only a handful to get a general grasp on what do others offer. But I didn't really find any story-heavy games among them. Maybe once YummySinpie releases her game? But it's been quite a while since any game-related news.
As to Selena, I too get why people would like to see her bigger. Personally I think she's hit that sweet spot between weight and personal comfort. And if I decide to make her gain more, it'll likely be optional. And probably won't happen any time soon. She's an important character and I don't intend to write any elements just for the sake of them. I treat these characters and world seriously even if you could say "hey, it's just a fetish game!". And with Selena romance... I think the writing's got to be careful here. Because like you said, they already have a fun dynamic of friendship and a mutual back and forth. Introducing romance can often destroy that. And then there's Ellie too. But I have a plan!!
About Liora... did you know she has a slim ending? You can actually push her both ways! And I actually have a different read on her chubby ending. She doesn't seem sad. She can take on plenty of strong warriors even with extra bounciness. What she gets is a permission to relax. A chance to step away from the grind and the anxiety while still staying on top. Though maybe I have conveyed this badly ahaha.