Welcome!! I'm sure you'll get a lot of support here!!
I just wanted to ask if you have met her? If not, is that something that you are interested in? I find that (for me) developing my own relationship with the "other lover" is important if I am insecure about it. That way, my mind doesn't run wild with me creating all sorts of images in my mind which aren't based on reality. Once I have met someone and have established a relationship with them (even if it is casual friendship) then I feel I'm in the loop.
There are situations, however, where I don't feel the need to meet a lover and I don't feel insecure about it at all, so I just handle each situation as they arrise and try to be aware of what I need in each case.