I had almost the same issue with my son. We did a different method of soothing when he woke up, but after several months, my son decided it was better if I stayed in the room and he wouldn't fall asleep. We ended up doing the cold turkey cry it out method. There's a book, "Healthy sleep habits, Happy Child", written by a doctor that talked about this method. I know some people think it's crule, but at your son's age, he's old enough to understand that you are not abandoning him. There are younger ages that this method is not suggested but at 8 1/2 months he's old enough to know it's not abandonment.
It took about 2 nights of the cry it out method, but he quit waking up at night. For a few months we had about 1 day a week he'd wake up, but we wouldn't respond and he'd fall back asleep in 10 or 15 minutes most of the time. We were so happy to have 4 nights of uninterruped sleep. Around 1 year he quite waking up at all and now we've had about 2 months of normal sleep.
I know it's hard to listen to your child cry, but I swear the cold turkey worked for us. It only took our son 2 days, but it might take about a week. We found if we kept checking on him every so often when he was crying, he just got angry when we left and got all wound up again. That's why we decided to cold turkey cry it out, and I am so glad we did.