Open Heart

What is the definition of Open Heart?  I am so confused with this.  A friend of mine told me that the definition of open heart is "someone whom you can trust entirely, won't feel that your are troubling that person by telling all your problems, will never feel the need to lie to that person." He said I just can't fully open my heart and tell someone or tell that somebody about my problem.  I don't know why.

But now, I think I know why.  I think don't tell because I know all the consequences that might happen.  I always predicted the worst before I can say anything, because I don't want that to happen, so I have to beware on what I gonna tell.  Maybe when I used this tactic for a long time, it becomes a habit and I can't help myself to throw everything out.  I think there is another reason, but I can't tell anybody of that reason, because I know if I tell people about the reason, then they will never tell me things anymore.  So why not I just keep everything myself and let them talk?  

I know that having a friend that always keeping herself everything is suffering because you want to care about her and understand her but she keeps standing at the protected area.  But I'm sorry.  I just can't tell.  

Sorry...