Regex to find string not followed by separator and 1 or 2 digits

I need to make a regex (.net flavour) that matches only "sometext" in the following strings (the second line has a space at the end):

sometext
sometext 
sometext dsf 2131
sometext-1234

but won't match anything in the following:

sometext  12
sometext 3
sometext2
sometext-1

That is it should match "sometext" only if it is not followed by any number of optional separator characters (like space, "-", "/", ".") and 1 or 2 digits (3 or more digits are fine).

I tried this regex with negative lookahead

sometext($|\W(?!\d{1,2}))

but didn't get too far.

I would use the following negative lookahead approach:

sometext(?!(?:[/.-]|\s*)\d{1,2}\b)

This pattern says to match:

• sometext match literal 'sometext'
• (?! lookahead and negatively assert that
  • (?:[/.-]|\s*) what follows is not a /.- separator or zero or more whitespaces
  • \d{1,2}\b which is then followed by either one or two digits
• ) end of lookahead

Demo