Given the complexity of the right-hand side integral, we recognize that the solution involves advanced techniques or numerical methods beyond elementary integration. Therefore, the simplified form of the solution is:
\[ -\frac{1}{y} = \int \frac{dx}{\sinh(3y) - 2xy} + C \]
\(\boxed{-\frac{1}{y} = \int \frac{dx}{\sinh(3y) - 2xy} + C}\)