Is it possible for a human to live happily forever alone?
Yes. I've just given a tech update to my students that deals with traveling at 'warp speeds', which is the only way humans would be able to form an intergalactic alliance. Sadly, it looks like this will never happen.
Even terraforming Mars is a very long shot and is uneccesary.
We'll max out at around 10 billion pepole and we have plenty of resources and energy for all to have a clean, sustainable world.
But the most important thing needed is 'to live happily ever after' we have to focus on our spiritual growth.
Basically, this means that:
1) We treat others as we'd like to be treated.
2) We use our talents to make the world a better place.
3) If you believe in God, thank Him for all that you have and ask him to assist you in creating the best world possible.