Backing away

I know already one of my flaws in a relationship is my backing away mentally from the person.
I have done it continuously in my past relationships. It is a defense mechinism so I won't get hurt or at least hurt to the extent that I have in my past. Reasons for me backing away very from man to man... but mainly if I feel like he's being distant, is not happy for the moment, is starting to act different or anything like that changes... I will start to back away... especially if I have asked him what is wrong.. and the answer I get~ NOTHING.
I am not as lovey dovey as I once was, I am not as quick to give as I once was, I try not to think of that person as often as I once did, I try not to show effection as I once did nor show that I am thinking of them or that I want to see them as I once did.
Most of the time this is short lived.. and if it does go on for more than a day- the relationship needs to be reevaluated and I need to make sure that this is something I want to be in and HE is someone that I want to be with. But most of the time its a day and then he does something sweet or romantic and I fall back in love with him all over again.
Its a vicious cycle that I play in my head, but I do it because of my past hurt and when I have felt like I have given my everything.. thats when I get hurt the worst.