The paper introduces a new formulation of statistical thermodynamics for classical fluids where molecules tend to associate into dimers and higher \( s \)-mers due to highly directional attractive forces. The authors break down the pair potential into repulsive and highly directionally attractive parts, expanding the logarithm of the grand partition function in fugacity graphs. This approach leads to a topological reduction, replacing the fugacity with two variables: singlet density \(\rho\) and monomer density \(\rho_0\). The thermodynamic functions are expressed as graph sums, and pair correlations are analyzed using a new matrix analog of the direct correlation function. The low-density limit is treated exactly, while the Mayer expansion, which uses only \(\rho\), faces significant challenges. The paper also discusses the importance of incorporating the geometry of the interaction early in the theory, aligning with Andersen's earlier work. The two-density theory is shown to be superior in the low-density limit, providing a straightforward solution compared to the complex graph resummations required by the \(\rho\)-expansion.The paper introduces a new formulation of statistical thermodynamics for classical fluids where molecules tend to associate into dimers and higher \( s \)-mers due to highly directional attractive forces. The authors break down the pair potential into repulsive and highly directionally attractive parts, expanding the logarithm of the grand partition function in fugacity graphs. This approach leads to a topological reduction, replacing the fugacity with two variables: singlet density \(\rho\) and monomer density \(\rho_0\). The thermodynamic functions are expressed as graph sums, and pair correlations are analyzed using a new matrix analog of the direct correlation function. The low-density limit is treated exactly, while the Mayer expansion, which uses only \(\rho\), faces significant challenges. The paper also discusses the importance of incorporating the geometry of the interaction early in the theory, aligning with Andersen's earlier work. The two-density theory is shown to be superior in the low-density limit, providing a straightforward solution compared to the complex graph resummations required by the \(\rho\)-expansion.