Confluence condition to track when deselecting a Item in a Multifield

[Masl]

Hello,

i have a num field which counts each time the user interacts with a multifield, to limit the max. options on a multi. Because the num counts everytime when interacted, it counts deselcted too. Now im looking for a Way to track when the user deselects an option to set the new Value. 

Is there any condition to use for this? Thanks