How can i stop these panic attacks?

Me and me ex are still gd friends, one of my only gd friends and he has moved quite a few miles away. he usually comes and visits me on the weekends but whenever he calls up and cancels (which yes, i understand he is within his rights to) i have awful panic attacks. my chest tightens up, i become very breathless and i have this strange feeling that something bad is going to happen or i am going to die (i begin checking my pulse repeatedly, getting people to feel my heartbeat) but for some reason when im like that i only want to talk to him, but when i call i get very panicky and upset on the phone and he becomes cross thinking im doing just to get him to change his mind. i'm not! im actually not too concerned about not seeing him, i'm worried about being on my own for the weekend. That feeling fills me with so much dread i feel like im having a heart attack. i know he doesnt really understand these attacks, and just thinks im being odd or selfish and its pushing him away but i dont know what to do?? :(