Hey folks,
It sounds like there are a couple different scenarios being mentioned here. For those where this applies, if you have a chance and haven't already done so, please head over to the AHQ thread mentioned here so we can gather more information to look into this further. Thank you!
"mightysprite;c-17920566" wrote:
This is a known bug. It happens when several sims are in a group conversation and someone does a romance interaction that can be received by the whole group, like telling a dirty joke. The romance bar goes up a little for all sims in the conversation, regardless of age or relationship to the joke-teller. Here is the link to click "me too", or submit a save as it's marked "Needs Saves"
https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVES-Group-Conversation-leads-to-inappropriate-love/m-p/9732350/highlight/true#M161588
The cheat codes you can use to fix the relationship bar in the meantime are also described in that thread.