I would start by examining what you mean when you say "CIO". Technically, I am not sure there IS a method called CIO. That is sort of a slang for the Ferber Method, and I think that a lot of people think it means one thing and really it means something else. So, perhaps if you clarify what exactly you are doing it would help us to help you.
With Ferber, you do not just put them in bed and leave them to check back in 10-15 minutes. And then at 15 minute intervals. No. What you do is put them in bed and check back at increasingly long intervals up to a limit (like 15 minutes). So, put them in bed, check in 5 minutes, leave. Check in 7 minutes, leave. Check in 10 minutes, leave. Check in 12 minutes, leave etc.. until you reach 15 minutes. If the child is still not asleep, you continue checking at 15 minute intervals.... and yes.... all night if necessary.
This is why it is often recommended to begin this on a night when you don't need to be up the next day fully functioning, so a Friday night for most people. The 2nd night should be much better. And usually by the 3rd night, the little ones are asleep before the first 15 minutes is up.
It almost seems to me that you are changing too much at once, though. If he has essentially been co-sleeping with you, trying to get him to go to sleep alone AND stay in bed alone all night, seems like a lot of change all at once. I have never tackled that myself, so perhaps other moms on here can suggest whether it might be better to address them one at a time, rather than just doing it all at once, or not.
If you did this with him last night, then tonight should be better.