I understand what you are saying better now. It is a lighter story, but I think there was a deep empathy, especially with the sister. She simply never wanted to engage MC in a serious discussion until the tree house because she didn't want to ruin the fragile reality they had built with each other. My impression was that if they did have a serious conversation that she knew that everything would come crashing down. To make a dated reference: she was Wiley E. Coyote running off the cliff. As long as she didn't stop and look down she could keep on running on air.
I don't recall Cory avoiding the uncomfortable situation because I thought their relationship developed with very good and healthy communication. They hit the uncomfortable situations head-on. Of course, the real stresses of a thrupple would come after the honey-moon period which we didn't really get to, but who wants to deal with those in a game?
As for Molly, I confess that I never played through to her ending. I enjoyed her at the beginning but I never regretted going a different direction when that choice came. Now, whenever I go back to play her ending I always slow down and go...why am I not with two super-hot volleyball players?
What I'm saying is that the genius of this game, and why I'm currently investing in Sumodeine futures, is that it is actually quite a deep game but with a light exterior. It plays like a light comedy and you can certainly just float through it and enjoy the ride like a lazy-river in a Mexican resort, but every character in the game has very well thought-out character motivations. I don't think I recall a time in the game where someone acted out of character for the sake of moving the plot forward or to get MC's dick wet. The most unbelievable aspect of the game is that all of these hot women would be so interested in a skinny nerd, but every story needs a little fantasy (and wish fulfilment).