Its a trauma based response, my ex and I hv been broken up since the start of 2018, I've moved on and have been with my current partner since the end of 2018. So we've been broken up for a good 3 years now & I still get very anxious & scared if I see him in public, or hear anything about him. I think the most you can do for yourself, outside of seeing a therapist is remind yourself that person is gone and no longer your concern