Made by a one person development team.
The game originally had a slightly different introduction that allowed the player character to be controlled while on the bus to Stardew Valley; there were several Non Player Characters on the bus that could be interacted with.
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.
Robin was originally planned as a romanceable character, but that was scrapped.
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.