I would suggest trying to get your users to move away from straight tables like what you're showing here. It's easier to spot trends in a quick bar chart. I have a screen shot below (from Qlik Sense) where I am showing year-to-date sales against prior year sales with forecast only showing from previous month forward. Each has a separate expression and the forecast data I am only bringing in the previous month forward, so there are not any historical values. If you have to have historical values, then I would suggest using set analysis in your expression to only show future months.
In your script you can copy the forecast and actual numbers into separate columns. In your pivot table create an expression for actual and another expression for forecast. Turn off the option to show zero values. That may give you what you need.