I know it is anecdotal, but I had this situation a few years ago. Someone I knew casually asked me in no uncertain terms if I was romantically interested. I told her that if I wasn't happily married (she knew I am married) I would definitely be interested, but I am happily married and want to stay that way. So I told her if she wanted to continue our friendship understanding that, I'm happy to do so.

I could have "bread crumbed" her, but that’s not my style. I also could picture in my head a "Bonnie Situation" (https://www.youtube.com/watch?v=idV4GQRflHM) exchanging a deceased minority from the original to a live woman who is not my wife.

We saw each other once more physically and then I never saw her again. It sucked cuz I liked her company, but she was obviously looking for something that I was not. C’est la vie.