these kind of things are much easier in VL:
- make a data type for a touch event
- as soon as you get a new touch point, create a new instance of your data type and add it to a spread
- when it disappears start a timer/monoflop or the like inside your data type to calculate a value to fade it out and eventually remove it from the spread
this is almost a 1 to 1 implementation of this particle tutorial:
only difference is that you calculate the alive value inside the particle with a timer and output it as a pin to connect it to the Keep of the ForEach loop outside.
does this get you started?