My envy/jealousy in our relationship? Please someone explain it to me

For reference: I am an ENFJ female/4w3 enneagram/Sun:Leo, Moon: Libra, Mercury: Virgo, Venus: Cancer, Mars: Aries

My fiancé is INFP male/3w2 or 2w3 enneagram/Sun:Leo, Moon:Sagittarius, Mercury: Virgo, Venus: Cancer, Mars: Taurus

Female mentioned (if it matters) is Sun: Libra (cusp of Scorpio), Moon: Taurus, Mercury: Libra, Venus: Scorpio, Mars: Leo

I am engaged to someone that I don’t deserve to be engaged to. He is wonderful- loyal, patient, and understanding. We are perfectly happy in a healthy way and realize that our relationship is not perfect and not without its quirks, but we are a great match for each other. I’m not sure if this is insecurity talking and fueling the fire, but I have this oddly weird feeling about a girl that he is still friends with. I have a history of getting gut feelings to drive me crazy and find out later that my intuition was correct. Most of the time when this happens, its involving a significant other and something that they are trying to hide for some reason or another. One time with an ex it was drugs/smoking, another time with a different one it was a girl, another time it was moving across the country and taking a job opportunity (without being told). The feeling that I have is the same whenever I suspect these things are going on and the individual could have done nothing suspicious and it will come out of nowhere.

My fiancé has several female friends. I don’t get these feelings with any of them at all. He initially said that he met this girl through an internship (a few years before he and I met) and that everyone thought she was really attractive and that they should date, but they talked about how different that they were from each other and were better off as friends. My gut kept bugging me and as time went on, I found out that he was initially attracted to her but he didn’t want to chase someone who wasn't interested in him. A friend of his mentioned that they had some kind of attraction for each other and there was definite flirting going on, but that was awhile ago. Yes, I understand that this is the past, but it must have been a big deal about her because he was even trying to fly down to see her at school (she lived in the south) and that is a huge deal because he is a homebody and never takes vacations or trips like that. Anyway, even now sometimes I feel like she is still a priority in his life. He is kind of messy, so I could see how he just hasn’t cleared his desk, but I see behind some of his action figures a framed photo of her and another person that they used to work with. Just her and an old lady. And he has some postcards from her. It could be lazy clutter, but weird that he has that stuff of her out of all of the female friends. He is going to do a run with her next month. I know that they don’t talk often (at least he doesn’t initiate anything) and I know that he doesn’t have a cheating bone in his body, but I don’t know what I am worried about.

I guess the scenarios in my head (because of how I wasn’t initially told that they went on dates and had a thing for each other and got conflicting stories) mean that maybe “she was the one that got away” and if she ever decided that she wanted him that I could lose him. Kind of like My Best Friend’s Wedding? Yes, I realize that I have a ring. I just don’t understand why he is okay with me being uncomfortable with this friendship he has. It’s not like they have been lifelong friends and I have no problems with his other female friends. So why does he hang onto a friendship that sounds like it has a weird romantic foundation to it? I also see the other side of it and I definitely don’t want to be controlling or anything, but I do want to fix the way that I feel to make both of us happy. If you can offer any help or insight or encouragement, please let me know.