AITAH for hooking up w my best friends ex

before they started dating i had a huge crush on him, but she’s more outgoing so she became friends with him for both of us and she ended up liking him too. he flirted / led us both on for a while and eventually picked her and they were in a relationship for like 6 months. me and her stopped talking as much during that time, and when they broke up she reached out to me and we rekindled. after a while of them being broken up he refollowed me on all socials, started hearting my stories, etc. and we hung out a few times and hooked up. she doesn’t know but i feel so guilty now, idk if im in the wrong though bc i had a crush on him first, i literally could not turn down the opportunity to hook up with him for younger me who had the biggest crush on him ever😭 they also just broke up bc she says he was controlling & manipulative and it made her lose feelings. so she doesn’t like him at all anymore, and she apologized to me bc she knooows she was wrong for dating him when i had such a crush on him for so long