Given a group $G$ acting cocompactly on a suitable simply connected cell complex $X$ with relatively hyperbolic cell stabilizers, we show $G$ itself is relatively hyperbolic. Building on work of Dahmani and Martin, the proof constructs a model for the Bowditch boundary by gluing together the boundaries of cell stabilizers. More generally, any cocompact action on a cell complex $X$ induces an algebraic \emph{complex of groups} decomposition which generalizes Bass–Serre theory in the case where $X$ is 1–dimensional. This model connects this algebraic decomposition with a topological decomposition of the boundary which we hope will be useful for answering other questions.