\documentclass[tikz,border=5pt]{standalone}
\usepackage[utf8x]{inputenc}

\begin{document}

    \begin{tikzpicture}[font=\tiny, >=latex, shorten >=5pt, shorten <=5pt]
        \tikzstyle{nonode} = []
        \tikzstyle{node_style} = [draw=white, very thick, circle, fill=orange]
        \tikzstyle{black_arrow1} = [->, black, line width=1]
        \tikzstyle{black_arrow2} = [->, black, line width=2]
        \tikzstyle{black_arrow3} = [->, black, line width=3]
        \tikzstyle{grey_arrow} = [->, black!50, dashed, line width=1]

        \node[nonode] (nAd) at (0,-0.1) {};
        \node[nonode] (nAl) at (-0.1,0) {};
        \node[nonode] (nBd) at (4,-0.1) {};
        \node[nonode] (nBr) at (4.1,0) {};
        \node[nonode] (nCd) at (4,1.9) {};
        \node[nonode] (nCr) at (4.1,2) {};
        \node[nonode] (nDd) at (0,1.9) {};
        \node[nonode] (nDl) at (-0.1,2) {};

        \draw[grey_arrow] (nAd) edge [bend left=10] (nBd);
        \draw[grey_arrow] (nBd) edge [bend left=10] (nAd);
        \draw[grey_arrow] (nBr) edge [bend left=10] (nCr);
        \draw[grey_arrow] (nCr) edge [bend left=10] (nBr);
        \draw[grey_arrow] (nCd) edge [bend left=10] (nDd);
        \draw[grey_arrow] (nDd) edge [bend left=10] (nCd);
        \draw[grey_arrow] (nDl) edge [bend right=10] (nAl);
        \draw[grey_arrow] (nBd) edge [out=120, in=-40] (nDl);

        \node[node_style] (nA) at (0,0) {A};
        \node[node_style] (nB) at (4,0) {B};
        \node[node_style] (nC) at (4,2) {C};
        \node[node_style] (nD) at (0,2) {D};

        \draw[black_arrow1] (nA) edge [bend left=10] (nB);
        \draw[black_arrow2] (nB) edge [bend left=10] (nA);
        \draw[black_arrow1] (nB) edge [bend left=10] (nC);
        \draw[black_arrow2] (nC) edge [bend left=10] (nB);
        \draw[black_arrow1] (nC) edge [bend left=10] (nD);
        \draw[black_arrow2] (nD) edge [bend left=10] (nC);
        \draw[black_arrow1] (nD) edge (nA);

        \draw[black_arrow3, shorten <=2pt, shorten >=2pt] (nB) edge [out=140, in=-60] (nD);
    \end{tikzpicture}

\end{document}
