Just need a opinion

If you saw your husband on social media and this female that you don’t know is calling him herb best friend and they are talking and every time you see them posting on each other’s page they keep calling each other best friend and you never heard him mention the female to you before. Would you question him who she is ? Or would you just let it go cause I am just trying to pick and choose my battles. Do you think a husband should be talking to another female calling her his best friend and hasn’t mention her to his wife?