I don't know that you'll ever feel "light" the way you once did again. Life and living comes with weight. Accept that you are going to keep changing and probably never be the same again. That doesn't mean you'll always be in despair, though. That, like the absurd, can be resisted.
One of the biggest problems in our society today is atomization. It strips away your humanity and adds to that despair. Reach out to others, find those that you can rely on and let them rely on you. (Healthy) Interdependence is the best way to have a strong, tight-knit community. Do what you can to help and make a positive impact. Doesn't need to be big or all at once. You can just build slowly. Make the world 0.0001% better every day and you're already doing great.
Make sure you live for yourself, too, and not just improving the world and forming community. Cultivate your tastes, find your hobbies, pursue not just your passions or the greater good but just things you enjoy. Despair comes from stagnation and rot, so allow yourself to grow and flourish.
You may not be light the same way again, but you can be happy and fulfilled. And maybe sometimes it'll be like it was before. And maybe you'll find that things get even better.