A gas engine needs 3 things to run. Fuel, ignition, and compression. Diagnose them individually.
Getting the right gasoline mixture can be a challenge, but starting fluid is volatile enough that it's MUCH more forgiving. So that means you have a compression or ignition issue.
Pretty unlikely to completely loose compression on all 4 cylinders so suddenly.
So you're likely down to ignition. That means more than just having spark. It has to happen at the right time. Within about 10 degrees and you should get a pop.
An EA82 will run on just the LH bank, as the distributor is driven off that cam, regardless of the RH side (I had a buddy that stopped at my house because his EA82 was even more gutless than usual, turned out his RH cam had seized). So you can assume that your problem is on the LH side. Unlikely that your ignition timing has changed considerably on it's own, but completely possible that the belt has. It's not terribly hard to pull the other timing belt cover on the LH side, and compare the mark on the cam pulley to the 3 lines on the flywheel. I bet it's jumped (I've heard of timing jumping as a result of bump-starting, so if it had a dead battery....).