It is however a very difficult one and I applaud your courage in tackling it. It strikes two of the things most dear to me, poetry and science. Some may laugh at that only failing to realise the beauty and elegance they both share.
So I'm going to have to be tough on the technicalities of both areas.

First the title
"The Neverending Story" is also the title of a very famous German fantasy novel by Michael Ende, also made into a successful movie. You may wish to reconsider it.

I'm picking up on some very tiny typos here because I think the poem is worth it.
The scientific corrections I offer you can choose to ignore under 'poetic license'.

planets,big and small, [space before big]

never clashing with each other [scientifically not true, not just asteroids and planets but whole galaxies collide spectacularly at times]

some are so a million light years away
perhaps
some are so many millions of light years away
or
some, a million light years away

or reduced to minuscule
perhaps
or reduced, minuscule
or
or reduced to a minuscule singularity

The tale of its wonders and mysteries
gave birth to many great minds in history
[these two lines are problematic to me, they don't actually give birth to great minds but ideas in great minds, or challenged great minds]

Altogether this is a wonderful poem and I think it is really worth re-working just a little.
I have recorded it for you to hear a different perspective-
https://soundcloud.com/user536630132/the-neverending-story-by

thrown some internal rhymes to break the prose sense of it.
however, I share jess that this is really a clever piece. I like it.

a typo as the universe continue[s] to spin its tale.

even tiny things like a space in the right place make a difference to the feel of a poem, eh.

I won't suggest specific rhymes though here is a handy tool for finding rhymes
http://www.rhymezone.com/

Did my reading help at all to give you a feel for the pacing/meter of the piece?

The fact that you are able to write such a poem and your choice of the theme while enduring pain is fascinating to say the least.

Be well soon..

Regards,

Been a long time since I wrote a poem dealing with space. But since you asked here's some ideas :
Stanza 1, line 2 I know this isn't meant to be a metered poem but I think countless might work better than myriad
Stanza 2, line 3 cycle doesn't seen quite right. I'd have simply said orbit
...............last line I'd change this to "their past being seen from earth" this will reveal that a great distances what we observe is what happened in the past due to light speed limitations.
Stanza 3, line 4 change to"or consumed" cleans the line up + reinforces the following line.
Stanza 4 line 1 Change bright to glowing (more accurate description
............ line 4 change marks to mark
............last line Try for new formation because nebulae can become stars, star groups or pleats
Stanza 5, line to delete many
This stanza seems to have one too many "tales" try replacing the last one with narratives or tomes.

As usual these are just ideas so be free to use only those you think might help or even none of them. I know it's a fought thing to write a poem dealing with the entire universe. Where does one stop? Should this include quasars, black holes, dark matter neutron stars,worm holes and all the other things I can't think of off the top of my head? But this poem does cover a good bit. One thing to consider as far as additional stanzas, how does the poem's content relate to you as an individual. Hope some of this blabbering is helpful........stan