Longtable and page break

I don't think that's possible with longtable, or any other tabular environment for that matter, because the material inside the tabular cells are TeX boxes, which by definition cannot be broken.

I suggest you use parcolumns instead, which has been designed to typeset several columns next to each other for multilingual texts. Here's an example:

\documentclass{article}
\usepackage{lipsum} % Used to produce long text
\usepackage{parcolumns}

\parindent=0pt

\begin{document}
\begin{parcolumns}[colwidths={2=0.74\textwidth},rulebetween,sloppy]{2}
    \colchunk[1]{\textbf{ID}}
    \colchunk[2]{\texttt{UC\_01\_01}}
    \colplacechunks

    \colchunk[1]{\textbf{Name}}
    \colchunk[2]{Password recovery}
    \colplacechunks

    \colchunk[1]{\textbf{\textit{Macro}-UC}}
    \colchunk[2]{Registration (\texttt{UC\_01})}
    \colplacechunks

    \colchunk[1]{\textbf{Actors}}
    \colchunk[2]{\texttt{ACTOR\_02}}
    \colplacechunks

    \colchunk[1]{\textbf{Preconditions}}
    \colchunk[2]{\lipsum[2-4]}
    \colplacechunks

    \colchunk[1]{\textbf{Main flow}}
    \colchunk[2]{Some itemize list here!}
    \colplacechunks

    \colchunk[1]{\textbf{Postconditions}}
    \colchunk[2]{\lipsum[5-9]}
    \colplacechunks
\end{parcolumns}
\end{document}

Just to record parallel package:

\documentclass{article}
\usepackage{lipsum} % Used to produce long text
\usepackage{parallel}
\parindent=0pt

\begin{document}
\begin{Parallel}[v]{0.4\textwidth}{0.55\textwidth}
    \ParallelLText{\textbf{ID}}
    \ParallelRText{\texttt{UC\_01\_01}}
    \ParallelPar

    \ParallelLText{\textbf{Name}}
    \ParallelRText{Password recovery}
    \ParallelPar

    \ParallelLText{\textbf{\textit{Macro}-UC}}
    \ParallelRText{Registration (\texttt{UC\_01})}
    \ParallelPar

    \ParallelLText{\textbf{Actors}}
    \ParallelRText{\texttt{ACTOR\_02}}
    \ParallelPar

    \ParallelLText{\textbf{Preconditions}}
    \ParallelRText{\lipsum[2-4]}
    \ParallelPar

    \ParallelLText{\textbf{Main flow}}
    \ParallelRText{Some itemize list here!}
    \ParallelPar

    \ParallelLText{\textbf{Postconditions}}
    \ParallelRText{\lipsum[5-9]}
\end{Parallel}
\end{document}