Scared that I will lose her again.?

I bonded with a colleague as her little boy loved me so much. I used to look after him and then a few months ago she suddenly stopped bringing him. I was very upset and worried that I had done something wrong and we didn't speak or see each other for 3 weeks. I asked to chat to her as I was worried and she agreed this and we arranged a time to meet. She didn't make that time so I contacted her and found out she was going through a bereavement. I felt very guilty that I didn't know and I know that I have stepped up to the mark as a friend. Now we seem closer then ever, she comes to find me in work to chat when she didn't before, texts me more and seems to want to be close to me. However I remember how awful I felt when she and her little boy suddenly disappeared and I am scared it will happen again. I am also scared that there was a problem which made her take her son out (even though she has brought him back several times since and still encourages us to bond). I am confused by it all. How do I get past the fear of this? At the moment I feel like I am walking on eggshells. Things are better then ever at the moment but I worry that may all end again and I will feel the way that I did back then.