Is it normal to get anxiety whenever i think about my ex ?

lately ive been thinking about my ex boyfriend a lot and i keep having flashbacks and remembering memories about him. I have an anxiety disorder so i tend to think a lot and worry about stuff but why do i get anxiety when thinking about him ?. our relationship was complicated, we both struggle with Mental heath issues and i guess he was kind of toxic for me. we brought each other down. i got way to attached to him, when i was with him all i wanted to do was be with him. i got major separation anxiety and i isolated myself from everyone but him. it was like he was all that mattered to me. my whole world depended around him. he never really fully broke up with me. we just kind of drifted apart , he says he was causing problems for me and my parents are strict and when they found out about our relationship they weren't to happy. even the school got involved. now every things changed. i haven't seen him for ages. i dont think he goes to the school any more. Im just wondering why i keep getting so much anxiety whenever i think about him ?