I am not saying advanced weapons , simply anti-tank and stinger missiles, nothing more or less so that they can stop the Syrian airforce and destroy their bases.
Already some rebel groups were supplied with stinger missiles in Aleppo and this helped them in Destroying Syria's main 2 main air bases there.
They are already separated , radicals have joined " Al Nusra Front " and those guys operate mainly near Iraq border and Damascus .
Simply both sides have a common Enemy and are utilizing all their resources to fight this common enemy , it does not make sense for them to fight each other as it will help Bachar .
FSA will eventually Fight Jabhet al Nasra because both have two completely different goals , the first are fighting for their country and the second fighting for " islamic empire " .