AITA for wishing happy birthday to the guy who liked me in high school.

Firstly, I apologize for any English errors as it's not my native language. When I (20 F) was in high school, I met Jason (21M), who quickly became a friendly classmate. He introduced me to his friends and helped me settle in after moving due to my dad's job. Although I saw Jason as a friend, he developed feelings for me. When he confessed, I kindly declined but agreed to remain friends.

Afterward, we got busy with exams and went to different colleges in different cities, losing touch as Jason wasn't active on social media. About a year later, during my summer break, Jason unexpectedly called me and asked to hang out. Curious and bored, I agreed. We met at a café where he eventually revealed he had a girlfriend, which surprised me. I asked if she knew about our meeting, and he confirmed she did. He then proceeded to boast about her beauty, so I asked to see a picture. I noticed she had a similar aesthetic and haircut as me, even after I highlighted my hair red. Jason proudly mentioned he showed my picture to his girlfriend and asked her to copy my hairstyle, which disgusted me. I left soon after, ignoring Jason's subsequent texts.

A year passed without contact until Jason created a new Instagram account and sent a friend request, followed by apologies for his past behavior. He claimed he had matured and apologized to his girlfriend, who forgave him. Despite my doubts, I accepted his follow request with the condition he not unnecessarily contact me. On my birthday, Jason called to wish me well, and I thanked him briefly. When his birthday arrived, I politely replied to his Instagram story, but I avoided further conversation by leaving his message on seen.

Recently, I received a furious call from an unknown number, who turned out to be Jason's girlfriend. She blamed me for ending their relationship, alleging Jason still had feelings for me and they had fought after he called me on my birthday. He promised to cease contact with me, but after I wished him on his birthday, he broke up with her to sort out his feelings. She criticized me harshly, calling me the cause of their breakup. While I'm relieved she left a toxic relationship, I feel guilty for keeping contact with Jason. Am I the asshole?