Well it had basically ended last year, Obama administration basically for the most part stopped arming them because it has failed. The rebels of 2012 no longer exist.
There are rebels fighting rebels, there are rebels now part of al-Nusra (al-Qaeda), ISIS, and a whole lot of other factions. There is no unified opposition and hasn't been for almost 3 years.
Arming opposition is one of the worst foreign policies ESPECIALLY in the Middle-east of all places. People criticised the arming of opposition heavily since day 1 and a lot of countries in the west refusing to do it but U.S and UK went ahead with it as usual.
The humanitarian envoy to Syria had strong words about the international community failing to create an environment for everyone to talk, they were more interested in arming and allowed the situation in Syria to happen for the past 5 years and now it's even more difficult than ever to get everyone to talk because of how fractured it has become.