Complex sentence: Chell is separated from Wheatley by GLaDOS and forced to perform more tests, but Wheatley manages to find Chell and help her escape to maintenance areas behind the testing chambers out of GLaDOS' reach.
Split into simpler sentences: Chell is separated from Wheatley by GLaDOS and forced to perform more tests. Wheatley appears in some tests, then Wheatley manages to find Chell and help her escape to maintenance areas behind the testing chambers out of GLaDOS' reach.