My (28f) best friend (30f) told me I was the fall back for my now Fiancé (29m). How do I even approach this?

I (28f) have been in a serious relationship with my now fiancé (29m) for over five years. Myself, my best friend (30f) and my fiancé have all been semi-close friends for over 8 years. Before my fiancé and I got together, my friend and him used to hangout more one-on-one. My friend and I were FaceTiming the other day and she was drinking. She confessed to me that one night, when they were drinking and hanging out, he hit on her and invited her into his bed to “cuddle”. She said that she denied him and she also added that they never did anything sexual together. She thought it was weird that he immediately iced her out and he decided to try me after she denied him. It worked with me and he hasn’t really spoken to her other than through me or about me.

I know my fiancé loves me but this has been bothering me and makes me feel stupid. I feel like he took his shot with her and failed so I am just a runner up. If she had accepted his advances, it’s unlikely that we would have ever been together. We have issues in our relationship (like any relationship does) and this makes me doubt his intent.

She is a beautiful lady and is a model. I, am certainly not. I haven’t brought this up to him yet because I don’t even know how to bring this up. It didn’t really hit until today and I feel so uneasy about the years that we have spent together, like it was all a front. I feel duped and used. Second best.

I need advice on how to bring this up to him without sounding as insecure as it makes me feel.

Thanks in advance.