War in my heart

So me and my boyfriend have been together for two years now but have been best friends for about 5 years. He is not my first love but is by far the best man I've come to love and know. I have been hurt and put through some traumatic experiences in my last serious relationship and was hurt very badly. I am completely over that but for some reason it feels like i can't fully open my heart up again. I want to and when me and my man are together I feel so connected and everything feels right. But when we are not together it feels as though my heart puts back up the walls and begins to question this love. I don't know how to fix this. I know this isn't how I'm suppose to feel so i try to put it away and tell myself all the reasons why I do love him. Anyways. Does anyone have an advice ?