Nearly five years ago, I separated from my husband of 11 years - my best friend and partner in everything since 1991. My son had just turned four.

I started tossing around the standard phrases like, "we grew apart," and "it's amicable."

I don't really know what happened (go figure, it's a little complex). It didn't work anymore, so we stopped being a couple. It was the right thing to do.

At the time, I didn't think all that much about what the future would look like. It was more about changing the present. I had no idea that five years later my son would have this other life that I know little about. That he would have siblings that I didn't give birth to.

When I was first contemplating the idea of separating, I couldn't imagine looking at his empty bed while he stayed over with Dad.

But I got used to it.

I cried when he went on his first airplane ride without me. I cried the first time he went away with his Dad for a week.

But I got used to that, too.

When my son's half-sister was born two years ago, I was a girl divided. One part of me was sincerely happy for the safe arrival of a beautiful baby who was so special to my son. Another part of me was devastated. I felt robbed, like someone had stolen my life.

Isn't it my job to give a gift this big to my son? My job?

But, follow along now, I got used to all of that, too.

The little angel is growing, and talking, and figuring out that I'm her brother's mom. (She's far too cute to dislike, even if I wanted to.)

Very soon my son will have another sibling "at Dad's house." Again I will feel cheated. Again I will feel old. I'm jealous. No doubt about it.

On the other hand, I will feel my child's joy, and excitement. I will smile with him. I will answer all his questions. I will understand that he is lucky to have siblings, for now, and forever.

Through it all, I'll be his rock.

Because I'm his mom. And that's all I ever need to be.