What caused your social anxiety to start?

For me, I was bullied pretty bad in 2nd grade of Elementary school and I’ve been dealing with it ever since. I am only comfortable/ myself around my few close friends and sister. I have such a hard time speaking to people I am unfamiliar with. I think my social anxiety got much worse after i was in an abusive relationship with someone who would talk down to me a lot and always had something negative to say about me, my appearance, what I said, what I posted on social media, etc. idk just wondering when everyone else started dealing with this shit