K.W.
At 8 months he doesn't NEED to eat every 3 hours-- esp at night--so he is just accustomed to waking up then and doesn't know now to get himself back to sleep. We all wake up in the middle of the night--it's learning how to get back to sleep that your baby has to learn and if he normally goes to sleep by you rocking him--they that the only way he know how to get to sleep. SO yes, you rocking him to sleep is the only thing he knows so when he does wake up, and doesn;t get rocked, he doesn't know how to get back to sleep!
So you need a plan to teach him to go to sleep and get back to sleep on his own. The basic Crying it Out is obviously not working for him or your and your husband--so I would try some variations that should ease him into the process of learning to sleep on his own, without you having to hear him cry for hours on end. It is a process though and really depends on the temperament and age of the baby at how long it takes to "train" them.
One or many posts on this site will give you a lot of DIFFERENT things to try, but what you need is one plan, and then to stick to it because CONSISTENCY is the the key here. Nothing will work in one or two nights--so trying one thing one night and something else the next is just going to frustrate everyone. So find something that you can commit too, and then stick to it!
(hehe, I've read so much on this subject since my infant did not want to nap/sleep either, but now I have a very easy to put to bed/nap toddler)
Read the following book: Good Night, Sleep Tight
http://www.amazon.com/Good-Night-Sleep-Tight-Helping/dp/B...
It's a great book that will help you and your husband devise a routine and plan to teach your child to sleep on his own--for some kids this comes easy, for others its a learning process all the way.
But read the book and see if it's something you can and want to do, then discuss it with your husband and commit to doing it. If you don't commit to this book there are a couple of other books/plans I would read and then decide on one to stick to.
There are two Baby Whisperer books that are similar but give you some different techniques that worked for us:
http://www.amazon.com/Secrets-Baby-Whisperer-Connect-Comm...
http://www.amazon.com/Baby-Whisperer-Solves-Your-Problems...
Unfortunately, you need to read both though since the first one will set you up with her techniques, but the second one really dives into helping parents with older infants and pitfalls they may have come across.
Babywise is what I read first, and though it is a great foundation, I found that it doesn't give too much leeway based on a baby's personality and doesn't give you any plans of action--just the idea of establishing a routine with eating and sleep and teaching the child by letting them Cry it out--yes routine with sleeping and eating is KEY. And sometimes CIO is the only way for a child to go back to sleep, but I found these other books gave some more in depth plans and techniques to use which made the process easier on both the child and parent.
Anyways good luck! I hope all of you find sleep soon!