Stardew Valley's newly released multiplayer beta also introduced a smattering of singleplayer content, not the least of which is the option to build Pam a nice new house. Players have been racing to work out the rest of the new content and, as Polygon spotted, made an awkward discovery in the process: in the beta update, if you woo everyone in town, your heartbroken partners will gang up, shame you, leave you, and then avoid you around town.
To trigger the group breakup event, you have to max out the heart meters for all the men (who'll meet at the saloon) or all the women (who'll meet at Haley's house) and give them all a bouquet, which indicates your interest in a deeper relationship. I can't decide what's worse: the public shaming or the disdain your ex-lovers treat you with afterward (thanks to u/irrelephante for capturing and sharing the brutality).
The specifics of the event are still being worked out, but it sounds like dating two or three people simultaneously isn't enough to trigger a group shaming. It may also be possible to avoid getting called out by only giving a bouquet to one person and leaving everyone else's hearts at eight.
Stardew Valley certainly isn't the first life sim to punish players for being unfaithful or promiscuous. Many players have pointed to visual novels and RPGs like the Persona games, which not only punish you for dating even a few people at once, but have been known to do so by having your irate partners beat the crap out of you on Valentine's Day.
Notably, modern dating games tend to offer non-romantic ways of maxing out a would-be partner's arc, that way you can stay friends with someone and see their story through to the end. Of course, Stardew Valley isn't a visual novel and romance isn't its focus, but a similar option wouldn't go amiss here. Many players who aren't fond of the update say they don't want to be forced to choose a partner and are calling for an option to marry multiple people. There'll probably be a mod for that.