\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
1 &=2\\
\intertext{aaa}
a+b&=c+d\\
\intertext{dont't forget that}
% use primitive display math here as a nested equation
% disturbs align counting
%$$1111=1
%\refstepcounter{equation}\eqno(\theequation)$$}
%0.5&=\frac{1}{2}
\end{align}

Second ``align'' environment is empty.

\end{document}

