do you mean when you hover over X you would like to show Y?
like a tooltip?
there are lots of ways to do this.
The easiest would be to use some nice CSS and I think position absolute.
try using the Bootstrap Tooltip widget for this:
It's easy to configure and offers a range of possibilities.
I think with your current setup you would be adding a tool tip to an entire column on your list. From your question I think you want to add a tool tip to each cell of the list. One way to accomplish that is to use a listview with the tool tips inside of it.
For this example I used a table inside the listview with the class "table-spaceless" so it has the look of a datagrid, and for the header I used classes "table-header" and "table-spaceless". Then I added the tooltip widget inside the list view. Now for my datasource microflow for the tooltip widget, my parameter can be the same entity type as the list view, and now I can show a tooltip specific to each row of the list.
For your case, if you want to show a tooltip for each month, you would need multiple tooltip widgets inside the list view.
Hope this helps!