I finally managed to draw the following path diagram with TikZ. Now, however, I am facing a challeging task. I would like to connect two edges/lines (here drawn in red; for the social scientists, I want to illustrate an interaction effect). How can I do that? 

![enter image description here](https://i.stack.imgur.com/wHcjL.png)

```
\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{positioning,mindmap,trees,shapes,shadows,calc,arrows,automata,decorations.text}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}[grow=left,
  line/.style={>=latex},
  coef/.style={font=\tiny},
  rect/.style={font=\tiny, rectangle, draw, text width=.49cm, align=center, node distance = 1.8cm},
  mycircle/.style={font=\tiny, circle, draw,  node distance = 0.2cm},
  beschrif/.style={font=\tiny}]

  \node[rect] (stab) {$D$};

  \node[rect] (zuf_m) [above left = of stab] {$S_m$};
  \node[rect] (zuf_f) [below left = of stab] {$S_f$};

  \node[rect] (konf_m) [above left = of zuf_m] {$FoC_m$};
  \node[rect] (konf_f) [below left = of zuf_f] {$FoC_f$};

  \node[rect] (unemp_m) [below left= of konf_m] {$U_m$};
  \node[rect] (unemp_f) [above left= of konf_f] {$U_f$};

  \node[rect] (behav_m) [above = 0.6cm of zuf_m] {$CB_m$};
  \node[rect] (behav_f) [below = 0.6cm of zuf_f] {$CB_f$};

  \node (error_sm) [mycircle, right = 1.3cm of zuf_m] {$\epsilon_{Sm}$};
  \node (error_cm) [mycircle, right = 2.8cm of konf_m] {$\epsilon_{FoCm}$};

  \node (error_sf) [mycircle, right = 1.3cm of zuf_f] {$\epsilon_{Sf}$};
  \node (error_cf) [mycircle, right = 2.8cm of konf_f] {$\epsilon_{FocCf}$};

  \path (zuf_m.east) edge[->,line] (stab.west);
  \path (zuf_f.east) edge[->,line] (stab.west);

  \path (unemp_m.east) edge[->,line] (zuf_m.west);
  \path (unemp_f.east) edge[->,line] (zuf_f.west);
  \path (unemp_m.east) edge[->,line] (zuf_f.north west);
  \path (unemp_f.east) edge[->,line] (zuf_m.south west);

  \path (unemp_m.east) edge[->,line] (konf_m.west);
  \path (unemp_f.east) edge[->,line] (konf_f.west);
  \path (unemp_m.east) edge[->,line] (konf_f.north west);
  \path (unemp_f.east) edge[->,line] (konf_m.south west);

  \path (konf_m.east) edge[->,line] (zuf_m.north west);
  \path (konf_f.east) edge[->,line] (zuf_f.south west);

  \path (error_sm) edge[->, line] (zuf_m);
  \path (error_sf) edge[->, line] (zuf_f);

  \path (error_cm) edge[->, line] (konf_m);
  \path (error_cf) edge[->, line] (konf_f);

  \path (error_sm) edge[<->, bend left=90, line] (error_sf);
  \path (error_cm) edge[<->, bend left=90, line, looseness=1] (error_cf);

\end{tikzpicture}

\end{document}

```