As a girl who’s been the recipient of this kind of situation (I was interested in him- he was single, though), it can send mixed signals and eventually lead to heartbreak. I’d say you should probably communicate with her and set healthy boundaries. I don’t think hanging out one-on-one is respectful to your significant other, plus it can lead the other person to believe there could be potential for a relationship in the future. Not saying you can’t be friends, just make your intentions clear
It’s fine to me as long as you can put up any boundaries whenever and not have them be weird. This girl flirts with me and my friends in a charming way that makes us laugh but she started doing that after I told her nah and we’re best friends now. I don’t really wonder if she still likes me bc I don’t like her but she is def my best friend. She checks in every now and then to make sure I’m not uncomfortable with the flirting too. My gf finds it funny