WIBTA Partners female friend asked to hang out 1on1 with him without me. How do I read this; is there an ulterior motive?

Looking for genuine advice. Long term partner has a female friend, who I’ve felt uncomfortable with but trying to shake it off by asking for more hangouts or events to know her more. But it seems she constantly asks for his audience or for hangouts with partners excluded. I’ve had previous encounters with her that’s robbed me the wrong way.

He has other female friends and they all seem to respect and understand boundaries, and have no problems involving or including me in hangouts. I don’t always attend but appreciate the gesture of getting to know them more.

WIBTA for having reservations about this specific request?