WIFI constantly disconnects when watching online stream video on my mbp
Try this quick-n-dirty solution.

Reset the WiFi


From toolbar -> Go -> Go To Folder
Paste this Address /Library/Preferences/SystemConfiguration/
Locate and delete these files


com.apple.airport.preferences.plist
com.apple.network.identification.plist
com.apple.wifi.message-tracer.plist
NetworkInterfaces.plist
preferences.plist

Restart your Macbook


You can read further for WiFi issues and solutions here