Try this:

(rn| )(denk|wil|dacht|kan|wilde|ben|zie)je(?=rn| )

The problem is that your original expression “consumes” both separators, at the beginning of a word and at the end of a word. If the separator at the end of the first word is “consumed” by the expression, it can’t be “consumed” by the expression that should match the second word. Using

(?=rn| )

performs a positive lookahead that only matches but doesn’t “consume” anything. You can write this even simpler, without having to use a positive lookahead, by using constraints (in this case beginning of a word and ending of a word):