DS is 6.5. I fed him to sleep, rocked him, co-slept (okay, admit it, I still do!). At one point - probably about the same age as yours, I couldn't take it anymore. Thought I should try 'controlled crying'. I put him down, said night night, put music on, left the room.
TWO HOURS LATER...he was still crying, by this time screaming, hyperventilating. He'd taken all his clothes off, was covered in sweat and by this time was whimpering. I just picked him up and he completely crashed.
I never tried controlled crying again. It just felt so cruel and so wrong.
I never 'cracked' the sleeping thing and I have never figured out whether it something you have to start from day 1, or whether some children just need to be with their parent/s to sleep.
So I'm sorry, I'm not much help with this one. All I can say is I feel your pain. But this phase goes SO quickly and I can now tell you that my ds is going to sleep on his own, he's a lovely, well-adjusted, confident little thing.
Hang in there.