The game treats romantic interests as seriously as it does marriage or going steady, especially if you have Generations and the romantic reputation system where any romantic interest can accuse you of cheating.
If you don't want your sim to continue the romance with the pregnant sim, you can go under mean interactions and "ask to be friends" and it will remove the sim as a romantic interest. The amount of green in the bar will take a hit, but at least that can be easily rebuilt with friendly interactions, and once they aren't romantic, no jealousy will be expressed. Even with the broken heart moodlet she may get, there won't be jealousy, just her periodically crying about their romance being over.
Be warned that if you do have the romantic reputations in the game, if your sim marries the maid but that other sim is still a romantic interest in the panel, there is always a chance your sim could be autonomously accused of cheating out of nowhere, and without cheats, that is a huge pain to fix without it ending in an autonomous divorce you can't cancel.