I completely get how you are feeling Eliza. I have the same sense of doom and injustice. I''m going to be alone for the rest of my life, never have the support or the companionship of a partner, and it feels unfair.
There is plenty to look forward to, and you''ll see it too when you get out of the messy practicalities (you will, i promise!) but the sense of incredible loneliness stays with me and keeps me awake.
in short, there is nothing wrong with you, but how to let go of that feeling, i do no know.