I met my best friend (Ella) in college and we've been close for 4 years. I love her like a sister and she's not my type at all. I've been dating my current girlfriend for a year and all three of us hang out once a week. Ella's boyfriend lives in another state and occasionally visits and all four of us will get together. I have always playfully flirted with Ella before either of us started dating our partners and she does it back so I didnt stop afterwards and I dont stop when we're all together. Last time we all hung out and I said something to Ella and added baby girl on the end in a silly voice and she said oh my God not in front of my bf and you're gf but her tone made it obvious she was joking. I don't know how her bf feels about it but I did ask my gf if she was bothered by the way that I speak to Ella and she said no. I'm wondering can I take my girlfriends word and know that she trusts me absolutely or AITAH for interacting with Ella the way we've always interacted even though there's nothing between us?