Show sources tell us Ariana found out about the alleged cheating in the last couple days and ended things with Tom shortly thereafter. We're told producers got word of what went down, and made the decision to fire up the cameras with the entire cast to document the fallout in the coming days ... and the hope is they'll be able to get it in the season currently airing.

What's interesting, Ariana was with Tom as recently as Wednesday to celebrate the release of his new single and perform with his band. However, sources close to Tom tell us the two have been on the outs for some time now.

In the promo for season 10 of 'VPR' it was suggested Tom and Ariana were in an open relationship, but Ariana later shut that down, tweeting, "We dont have an open relationship. i'm really not that cool. thought that was obvious. bisexual ≠ polyamorous."

However, it's been a storyline this season that Raquel has wanted to hook up with the show's other Tom, Tom Schwartz ... the two made out at Scheana Shay's wedding.

Tom and Ariana first got together back in 2013 when she joined the show as a full-time cast member.

Neither Tom or Ariana has addressed the split or what led up to it publicly ... though Ariana deleted her Instagram account.