I believe is more than just being a potential cheater. Men and women that constantly scan the room, walk around, look at others do it to make the partner they are with feel uncomfortable and to create a feeling of insecurity/jealousy. Some do it to get a reaction out of you, test your boundaries, if you are paying attention to them, or have other people think they aren’t with you. From my extensive (long term) personal experience, this would be a deal breaker. Big red flag. I would end things with them immediately. Like i would leave them standing there, and text them good bye and have a nice life.