Teddi Mellencamp is spilling the tea on her affair with horse trainer Simon Schroeder … confessing she can’t help but wonder if her stage 4 cancer diagnosis is karma for her past missteps.

On “The Jamie Kern Lima Show” podcast, an emotional Teddi made it clear she definitely hurt people, including her kids, when it came to the affair that made headlines last November, just weeks after her divorce announcement from Edwin Arroyave — and that still breaks her heart to this very day.

Teddi elaborated through tears … wondering out loud if her cancer diagnosis was the price she had to pay, saying, “Nothing goes without payment.”

No doubt the affair was a mess, with Simon Schroeder’s ex-wife, Karli, filing for divorce on December 30 — just weeks after the scandal broke. But Simon? He’s kept quiet about the whole thing.