In other words, how can I forbid pagination between \myenv and \endmyenv? I thought at first to make the whole thing a box; if I'm not mistaken---this would prevent TeX from breaking it up---but I don't know how to do that in an environment...environment.
I have a not-MWE, but I feel like this question is sufficiently general that it doesn't need one; it may even be a duplicate that I failed to find.
minipage, e.g\newenvironment{myenvironmnet}{\begin{minipage}{<width>}}{\endminipage}