Student or Learner
M: Finding out about Angela and Molly really made his heart sick: the lies, the breaking of the law. This will be so much worse. (Here "this" means finding his mother is actually another woman.)
A: On top of the little matter of Piggy Brown. We'll have to wait until that's over anyway, for better or worse. (Here "that" means the little matter of Piggy.)
My question is that the phrase "on top of" means "in addition to" in the context? Or it has a different interpretation? Like "finding the truth about his mother is so much worse than the little matter of Piggy?"
It does mean 'in addition to', but 'top' could suggest that this last problem is so serious that nothing else could come after it.