it depends on the terms of relationship...
solution is to confront her and get the answers...it always take time to accept the truth...you know.
All the above have said it, it all depends on the relationship. My own situation is it has to remain secret but I know I am very special to him even if he does not say it. Before we got into this I knew no one could ever know the truth as if it got leaked to the wrong person there would be big trouble for him and for me and we could both loose the roofs over our heads. SO it remains between the two of us which is hard as I would love everyone I know to meet him but that's impossible but no one ever said what I am doing would be easy so I only have myself to blaim.
if they keep it from you because they think it will hurt you then yes
It depends on the situation... they could very well love you. but someone in their family may be against the relationship.. for whatever reasons. Your poor friend may not know how to go about telling them... it's a constant struggle... they want to please everyone... Tough situation to be in. But don't worry unless they tell you it's Over. Then Just Relax.
It depends on how big is the secret
In some ways yes. Depends on what the secret is. And what he's keeping you from.