My sister is the complete opposite of me. She grew up wanting her own family and through a series of events beyond her control the closest she'll ever get is being an aunty.
For a good few years she floundered, it really took the wind out of her sails and yes for the seemingly uncomprehending made her feel as though her purpose was never going to be realised so what was the point in trying anything.
I'm happy to say that she's out the other side now. She's taken up a hobby that is incredibly fulfilling, enjoyable, time consuming and which also led to her meeting her now husband. She travels all over the place experiencing and regales my children with her adventures.
This isn't the life she desired, but finally it's a life she's living rather than just existing in.
You have two ways to redirect your energy and purpose in life. Towards helping children who need it most through charity works, fostering or respite care.
The other would be by embarking on a new version of your life that sees you making the most of adult freedom by travelling, taking up a hobby, taking up a sport, campaigning for matters close to your heart...anything really that makes you take a deep breath and be satisfied that it's time well spent.
I'm sorry that this isn't the version of your life that you wanted. I'm not living the life I desired either, but you do find new ways of seeing the sunshine and having purpose beyond your original plans.