Made by a one person development team.
ConcernedApe put out a couple of Twitter polls to decide who to make as eligible marriage candidates in a then-future update. Shane and Emily were the winners and were later made romanceable.
The beta versions of the infidelity scenes were initially much harsher. In the 1.3 update, being caught dating every bachelor/bachelorette at once will cause them all to be angry at you and refuse gifts for a week, but then return to normal.
Robin was originally planned as a romanceable character, but that was scrapped.
The character of Alex was originally named "Josh", and was unveiled to the game's followers as such in the dev update introducing all the bachelors and bachelorettes. The reason for the name change is unknown, but his house is still referred to as "JoshHouse" in the game's files.