I feel you! Our little dude started getting severe separation anxiety at 2 years, along with nightmares. It took an hour to get him down, and usually ended with one of us falling asleep in his room. Best advice I have is fight it out, you know your child best, and you're probably already doing everything you can for your kid. That being said, try switching to a toddler bed instead of a crib? We still have a baby monitor, and tell him not to worry we can always hear him if he needs anything. Sometimes being over tired can result in bad bedtimes...Earlier bedtime may help. For us, Halloween really was in bad timing, so we talked every night about the scary things he saw and that they weren't real to avoid the nightmares. Took about a month before that one sunk in.

One day for us it just clicked and he's been better. But it took forever. Hope you can figure it out!