Well i have fairly low self-esteem so whenever someone flirts with me i think of all the worst before i realize gee maybe this guy likes me. anyways everytime someone like me i kinda become a "female dog" to them and i sort of push them away. I never noticed it until i did it to someone i really liked. It's not that i don't want a relationship or anything so is it normal?
You obviously have very low self esteem and you should fix that. One day you will find someone who loves you with all of your flaws, whether fixable or not.
You are afraid of getting hurt and you are protecting you feelings, which is normal. Try to analyse the person you are with and see if yo can imagine them in your future and ask yourself if he is treating you right, because the right men are so rare. Perhaps if you are open in your relationships you might find it easier to express yourself as you know that they know what you are feeling.
I hope this makes sense. It is hard realising that what you had was great after you have lost it.