The most common and most likely answer to this crossword clue is the 9 letter word LIMITLESS
L
I
M
I
T
L
E
S
S
More clues leading to the result LIMITLESS
Buddy explains!

The straight part
We know that "going on forever" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case going on forever = limitless.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LIMITLESS mean?
LIMITLESS adjective- Without limits in extent, size, or quantity; boundless.