From Wetpaint.com: Does Stefan Have a Right to Be Angry About Damon and Elena?
Ever since The Vampire Diaries Season 2 premiere when Stefan found out that Damon thought he had kissed Elena — though he actually kissed Katherine — the tension within the Salvatore brother love triangle has been mounting. But up until Stefan skipped town with Klaus in Season 3, Elena made her feelings clear: She loved Stefan. She chose Stefan. And even after a very passionate front porch kiss and an even more passionate motel makeout with Damon, when asked, Elena once again chose Stefan.
However, that all happened before she became a vampire, was sired to Damon, and effectively broke up with Stefan only to sleep with Damon (twice) less than 24 hours later. So does Stefan have a right to be angry? Yes… and no.