I'm with you all but didn't expect such a unanimous rejection, considering how the conversation goes in threads - maybe it's mostly trolls fishing for reactions, knowing that a lot of people feel strongly about this?
As a happenstance with no impact on the story, it feels gratuitous. As something designed to have an effect on the player I can't see how it's not aimed at humiliation, even if it's framed as "mild" and the couple goes on well despite it. Two games immediately come to mind that have been flirting with this, or already have the mechanics in place: one is Family Vacation and the other is Life at Windvale. Don't mean to post some back-handed criticism and would love to hear from the authors if they checked this thread, but understand if they need to keep a balanced stance especially before their support base.
I can't see it in a positive light, but I see myself on the extreme side that doesn't like when sharing leads to any of the LI's "firsts" (first kiss, first sex, first anal, first whatever) being "taken" when she's in a relationship with the MC - let alone getting impregnated by another guy.