How to cancel voice so ties are right direction

[Jeff Barnes]

This snippet illustrates a problem I'm having. The tie on the g is in the wrong 
direction after I've finished with the voice split. How do I get the correct 
tie direction? It looks like the \voices are still in scope wrt ties.

Also, why did I lose the \relative c' after the voice split?

\score {
  <<
    \new Staff {
      \relative c'
      <<
        {
          \voiceOne
          g'2
        } \\ {
          \voiceTwo
          c,2
        }
      >>
      <g' c'>4 ~ <g' b>
    }
  >>
  \layout { }
}