Do we really know each other!

A friend I have known for over 20 years and we are great friends and we still keep in touch. When my kids were little we were heaps closer and our partners were great friends but they fell apart, so it kind of made it hard on our relationship and we became distant too. We still spoke on the phone and met up every now and again, but is not the same as having BBQ's, going camping, our families hanging out together!
But we have always remained friends and I can actually remember times with her, and you know me my memories are very limited! She can tell me stories about my kids when they were little that I had forgotten and she can remember the littlest of things which is amazing!
But we had a talk on the phone the other day and we normally talk about ME and my family and all my problems! But this time we got talking about her family and she told me some major stuff going on in her life! I was so shocked and surprised and I was so intrigued with what has been going on in her life that I wanted to hear more.
But sadly it made me realise that I was wasn't really a part of her life like I use to be. Our boys are the same age and I can only ever remember going to his first birthday, she has a little girl and I have only seen her once and I am sure she will be 4 this year! She missed the most important day of my life and I truly understand why she could not be there, but it still hurts.
But how do we allow this to happen? It made me think that even though we have been friends since high school, I don't really know the important things going on in her life. This made me sad and made me realise that I have so many friends and it is hard to keep on top of them all and I need to keep in contact more with them.