There were at least two instances where Silvio kind of betrayed Tony.
1. He felt a way about Tony making Christopher his #2 guy in season 4, and was actively undermining the Esplanade deal (gave Patsy the OK to continue stealing from the site).
2. When Tony got popped Silvio and Paulie weren't giving Carmella any money. They only showed up with bags when Tony's condition improved again. They smiled in her face but Carmella caught them scowling when she turned her back to them (can't remember if it was in a reflection or something).
I feel like there's a third betrayal that I'm forgetting about.