Story
Overall it I think it was OK - at least enough for me to want to read the entire thing :). My main criticism is a sore lack of exposition in general. I feel like the genre does best when you genuinely know the characters, enough that you pick up on even minor behavioural changes. As it is, the prologue had things progress way too quickly. I'd have liked loads more text, even if only the first half of the events are in the prologue. Introducing the characters more and their daily lives before things start really happening.
When Davis comes to give you a report, there's a line about how despite appearances he's skilled and trusted, why? Why not a quick anecdote that showed more of his character, e.g. handled a very tricky customer after taking them drinking, upstaged a senior worker using his charisma etc. Davis got married a week before the player joined, "loved nothing more being asked about his new wife" yet a month later he's not even shown his wedding photos to the player?! Can we get a little more about why he might not be 100% satisfied with his relationship and what he likes about Fiona?
I'd have liked to see the couples get to know each other much better before suddenly doing double date -> weekly swap double date. I mean, there was like 50 lines of conversation between them over dinner and the date. Not much of in the way of player thoughts either. As a rusult, felt very unreal imo. I'd have liked it slower, say after a few times of "normal" meet-ups Davis starts to do slightly bolder things each time, maybe you noticed Fiona looking/staring at Davis or Kyleigh etc. Perhaps the guys share a common interest or pasttime, or even just drinks after work, gradually get closer to best friends before talking about the swap double date.
Sex scene was.. not great. Art was OK. Text, well, there was like 10 lines... way more detail please! I want to read more of the player's thoughts, especially about Fiona's more assertive behaviour and the inner conflict that might bring to him. What about her emotions and expressions?
Characters
Protagonist is a "Department manager in an office", why can't he have a real job?! Even if it a generic ACME, telling us a little about where he and Davis work would help immersion. Player had his doubts about the job move, does that mean he did poorly at his last job? Shitty boss, long hours? Maybe the new jobs is simple high stress/responsibility position? He's not sure Fiona would have agreed to move if he wasn't confident, he didn't share her doubts with her - why! Does she not have confidence in him? Has something happened before? Where/how did he meet Fiona? Does he think he's not worthy of her? What does Fiona do during the day - we know she's a housewife who is good at cooking, but is she involved in the neighbourhood, does she like gossiping with her friends or just watch TV all day? Does she have friends! What are her likes and hobbies? Is she picky or fussy about something? Maybe she hates being alone. Are there any signs she's not happy? Her thoughts on having children? Ditto all this with the other two (though I guess maybe you want to save that for later in the story).
Technical
Character sprites should be zoomed in more, especially in one on one conversation. Super weird to see Fiona so far away when you're supposedly across the table from her having dinner. Think this would help notice expression changes too, they aren't too obvious at the moment.
Text needs to be a little lower in the text box, comes really close to overlapping character names.
The options along the bottom are
reeealy tiny. Windows 10 x64 if it makes any difference.
Absolutely needs a right click -> hide text window option.
Ideally needs a text window opacity slider.
History sometimes gets a bit
messed up with overlapping text.
About page should probably have a link to your site/Patreon.
No music!