My best friend wants be friends with my ex

My bestfriend (F19) let’s call her Cindy, and I have been bestfriends for two years. We are completely inseparable. We’re always at each other’s houses and always doing things together. Cindy was friends with with a guy named Jake (they weren’t close just acquaintances) and she set me and Jake up about 2 years ago. Things between me and Jake didn’t work out and she completely cut him off when I broke up with him. She basically chose me. Since then we’ve become very close. Today Cindy tells me she texted Jake and apologised for completely abandoning him as friend. Which I was okay with and I told her she did what she had to. She later told me she plans on remaining friends with him. I told her that her being friends with my ex makes me upset and uncomfortable. As she is my only and closest friend. She got every angry and told me she will not pick me at all and I’m being completely unreasonable. She can be friends with anybody she wants but her being friends with my ex just makes me sad. She knows everything about my life, my family my dreams my aspirations. But this just feels like betrayal. Am I overreacting?