In short, how do you shake it?

My husband of 20 years and I recently decided to move from an open relationship into a poly relationship. A friend of ours approached us and showed an interest in getting to know and date us both together and as individuals. The issue I'm finding is that she is (on paper) a much smarter match for my husband. More shared interests, similar jobs, she is wicked smart and pretty, thinner than me, nicer body, better cook, ect. My husband and I were in an open relationship for over 15 years and I never had any issues of jealousy. I know my husband loves me and that neither of them would intentionally do anything to hurt me. I have spoken to both of them about this and have been heard and reassured multiple times. But the addition of the prospect of feelings/love have made me insecure. The rational part of my brain knows that these are issues I have made up. But the scumbag part of my brain won't stop comparing us and reminding me that I come up lacking in every category. I do speak to a therapist weekly, am on antidepressants, and plan to ask my therapist about anti anxiety medication as well. But in the meantime, I would appreciate any and all advice or wisdom from the collective as to how to get out of my own way on this. I don't want to ruin the beginning of a very good potential thing.

Thank you.