We're the Last of our Siblings without Children. How do others who can not have children deal with this?

Would it make you feel better if I told you I am the last of our siblings without a husband?

All my siblings have been happily married and I don't even have a boy-friend. At least you have a husband to be on your side to comfort you. I am all alone.

Two ways:
(1) Cognitively
(2) Behaviorally

(1) Cognitively:
It is always easy to idealize a situation that you are NOT involved in.
Children bring happiness, but also great sorrow. There is an old saying that "Every child has its own brand of tears for the parent".
It is also helpful to remember that sociological studies show that couples WITHOUT children measure higher on happiness scores (both general and marital happiness). And that couples without children have more financial resources and less financial stress/worry.
Understand too, that your emotions are caused by your attributions and cognitive self-statements ... what you tell yourself CAN hurt you (emotionally). So pay greater attention to your self statements. now you cannot successfully pretend that you are happy to not be getting pregnant, but how you react to that fact IS under your conscious control.

Additionally, your guilt about your sorrow is self-created. She is happy, but you aren't trying to make HER feel guilty .. you are harming only yourself by feeling guilty. And there is no reason to feel guilty because you want children yourself.

Lastly .... no one IS going to ask you about things that make you sad. It is considered unkind and poor social form to bring that kind of topic onto the table or discussion. Your sorrow is for you and your husband to deal with. Don't expect others to flock to it.
As an adult, it is up to you to take responsibility or your own feelings and now play victim in your family.

2) Behaviorally
You develop relationships with your nieces and nephews.
By babysitting as often as you can.
If they do not live in your area, then when they are older, you invite them out for a week or two once a year (my daughter has a great relationship with one of her childless Aunt & Uncle .. and this couple takes each of their nieces and nephews for a week one at a time, every year).