Caught hubby texting my sister?

I recently found a series of flirty texts between my husband and my sister. I haven’t confronted either of them yet because I’m unsure if it’s harmless or something more serious. We are all very close, and I’m worried about causing a rift in the family. How should I approach this situation without jumping to conclusions? Any advice? #WhatWouldYouDo #FamilyDrama #TrustIssues