What I found interesting about the wedding dress event was Liam's unprofessional behavior. Of course Cathy had a dream figure but should be constantly surrounded by women like that at work. He's there as a consultant and he's acting like an immature teenager. The woman wants to get married and he takes the opportunity to check her out. Maybe a coincidence, maybe L&P is again a reference to the character of Liam.
As for the invitation from Cathy, I don't believe in the beginning of a swinger route. Again: They want to get married (!) And suggest swinging to a couple of friends? I think the invitation is used to propose to Sophia and Liam how to organize the bachelorette party. Sophia for Cathy and Liam for Andrew. On both the Good-Wife Route and the Filty Route, these parties could start separately but maybe end together in a club. Then maybe swinging would be possible with a lot of alcohol. The parties could just as well stay separate and Sophia and Cathy have fun with the strippers.
Well if The Oracle says so, it must be like that
Jokes aside, maybe I got carried away by this new pacing of the game. Asking to be the best man/woman and organizing the bachelor(ette) party it is likely where it is headed.
The swinger thing it was more because they seems the "candidate couple" for that, especially after what we saw in the dressing room. And again I was suggesting that if it is the case the things will be set in motion in some way, not explicitly but preparing the field for that to happen either at the bachelor party or whenever.
The fact that they want to get married it doesn't mean that they are not into it, we don't know much about them but it won't be that bizarre they are into the swinging life even before marriage.
If Liam is cheating on Sophia I wonder which one will get caught first?
Or could it be that Sophia pressured Liam into swinging and he is not happy and ending in divorce.
If Liam is cheating and I hope that he is not as I think it would reduce the impact of the ending.
I don't know, my impression after the dress event was more that there is a hint that going on with the FW route Sophia will get involved in other things, maybe even "pleasurable" for her, but that will have a price to pay in terms of her marriage.
Liam's interest for Cathy seemed to me a sort of "warning" for what would/could happen down the road. As a paradox, Sophia will start to neglect Liam or even her close friends leaving Liam falling into temptation. So for me is not that Liam will cheat right away but that could happen down the road as a "price to pay". To answer your question, for me it will be as soon Sophia will start cheating on him, everything will be in place for Liam to do the same, leading to the failure of everything etc etc
Again it's just an impression I had playing just for the first time yesterday.