He Sneak Peek On Her

We are 29 and 28 and there is a nice couple in their 50ies in neighborhood, last week we went for a picnic. My wife was wearing deep neck top and I noticed my neighbour was starting at my wife’s whenever he get a chance to sneak peek..
His wife is sweet lady and I don’t think she noticed this at all.. I also noticed he touched my wife many times over her shoulders and my wife told me he even pat her hips once.. she told he seem pervert abs we need to make a distance from them..
The main issue here is, I was not angry in him but excited, then I started looking about this behavior and found couple websites like this.. surprising this looks like much more common than what I thought..
What should I do ?? I am unable to get sleep and getting many different type of fantasies.. please help!! I need someone to talk this it’s getting over my health now..