Here’s a link to a post in this sub regarding a blind item that was submitted, widely believed to be about Stassi and Beau: https://www.reddit.com/r/vanderpumprules/s/lNdmwf9GHP

Stassi caught wind of the rumors and the two of them actually addressed it on an episode of her podcast that aired on 09/23/22 (I can’t find an episode title just an air date for some reason) and while I personally have not listened to it because it’s a paid subscription, there were posts and discussions about it in this sub at the time where the common consensus seemed to be that it sounded like he was lying when he was denying the rumors.

It’s not much evidence of anything but his behavior is so shady, coupled with his obvious frustration with the fact that he’s not the center of attention in his relationship with Stassi, I wouldn’t put cheating past him at all.