Look at your friends from a different angle. If your house burned down and you needed a place to stay until the insurance money came, would your friend let you stay there unconditionally? The person who will give you the shirt off their back to ensure you are warm without asking for anything in return is a friend. Anyone else is just periphery.
It's a hard lesson to learn. I have this need to be liked by everyone, which means that sometimes I have unhealthy relationships with people. It takes a while to see it, but eventually I do. It is hard to cut those toxic people loose, but eventually it has to be done.
I know I don't know you that well, but from your posts I can read that you are an intelligent and very caring person. You deserve friends, not periphery.
It may be a good idea to step out of the crowd and get together with a few of your closer friends from that crowd on the side. It's not that you are asking those friends to choose between you and the other woman, you are choosing to engage in activities that are healthy for you. If they are your true friends, they should understand your position.