I wanted to make a system where if the mouse hovered above a tower it will show a "upgrade" button. I got that working, but the button would stay there forever. is there any way to get the button to be destroyed once your cursor has passed it?
Right click and invert the condition.
To be more flexible, I recommend utilizing an invisible helper sprite to define the area where the the popup stays visible instead of using the objects themselves. This will allow for more flexibility in placement of the popup, as well as stave off issues when you have multiple or other objects creating and destroying the same popup.