My whole life my family, friends and boyfriends have let me down and left me. Now i am in a relationship with the most wonderful person in my whole world.

We have been together for almost a year and a half. I know he would never leave me, and i know he loves me unconditionally, but even when we get into the smallest of arguments or bumps, i panic.

i don't understand why i do because i know he loves me and that he wouldn't ever leave me. He's proven to me and constantly reminds me that we will grow old together and that he will never go away. I think it might be because my previous boyfriend (a complete *** and ignored me but i still stayed, stupid me), he and I went through a rough patch and he wouldn't let me in to try and fix it, he just ignored me then broke up with me over the internet (jerk.) So many friends have done things similar to me also, so i suppose i just sub-consciously assume that in time he will as well.
What do you guys think? Why do you think this happens? I need to learn to stop freaking out and having a mini panic attack every time we even slightly don't get along. Do you guys know anything that may help?
Thanks,
missminnie