Am I in over my head???

Hello everyone!! I recently started talking to a woman who is in a committed relationship with a woman but they're both poly.

I first met her partner at a concert and soon somehow ended up talking in her. It's hard to wrap my head around the fact that i'm trying to date my (sorta) friend's woman!!!!!

I have never been the type to turn down experience, you know? But there's a lot i'm not sure how to go about because i'm used to regular smegualr monogamy after all!!! though, I'm so open to this and i've even had my own moments where I questioned whether I was poly.

She's pretty and sooo smart and I'm just thinking can I really fathom the fact that she wouldn't be completely mine? Can I interact with her partner without being weird???

Please any tips and knowledge you're willing to spare! would be amazing.