"He rehashes the affair on the phone with her every other day," one of his pals tells Us. "They fight, but they are back together."
So, why doesn't Rob just move on? Are K.Stew's lickable armpits really that irresistible?
"He started thinking nobody else would understand his life," sighs a source. "His rational voice told him not to toss a three-year relationship for one infidelity."
Adds another spy, "They have a very deep connection. Plus, they're young. All relationships at that age have drama."
For now, says Us, they want to keep the reunion "on the down-low" (alas, that ship seems to have sailed) because they're worried about the blowback from fans.
The stars supposedly plan to wait a few months before making it clear that Robsten is indeed unbroken, a timeline that should coincide nicely with the promotional blitz surrounding the Nov. 16 release date of "Breaking Dawn -- Part 2."
Keep clicking for photos galore of Rob and Kristen together ...