Im the same, my ex dumped me out of the blue he was a total head **** and made me insecure etc. With my current bf im clingy, if i see some random blonde or pretty girl commeont on facebook i get upset, i know it is my own insecurities that cause this as all the time i am afraid he will leave me like my ex did.
For advice pinpoin in yourself why you feel thsi way, is it because something happened, someone said something to you, then have a talk with your bf and tell him you find it hard to trust him or whatever, i didnt for ages and my bf thought it was because i didnt love him etc and was portraying him wrongly. I saw a councellor about other matters and it all came back to my own insecurities which i had to work on myself. A reltionship is built on trust, tell him how you feel i know it is not nice at all to feel paranoid.