WHY every time I think of her I cry

So my friend is pregnant. She is officially 14 weeks as of last Friday. We already knew for a while; well, maybe not knew but definitely suspected. She stopped drinking a while ago, and recently would abruptly change the subject whenever anyone mentioned a baby or a pregnancy. It was clear.

We got pregnant before them and encouraged them to start trying so we could be pregnant together. Now she is pregnant and I am not.

I am happy for them, very, very happy, I really am! So WHY every time I think of her I cry?!

Is it because she is already 14 weeks, and I don't even know how it feels? Is it because she will read my pregnancy books even before I will? Is it because they will already have their baby when we only will be able to start trying?

It should be me! I should be 14 weeks, heck, I should be 33 weeks now! I should be deciding on the baby's name! I should be the one who answers all the pregnancy questions, not the one who asks!

I thought I was over it. I don't cry when I see babies on TV anymore. I look at my pregnant cousins pictures and smile. I even went to another friend's baby shower and wasn't sad at all. So WHY every time I think of her I cry?!