You need to do some sleep training. It needn't involve leaving your baby to cry.
I had a similar situation at 8 months, when I was stuck in bf my dd to sleep. Every time she came up into light sleep (i.e. hourly) she realised something was missing and wailed.
First thing is to make sure you have a good sleep routine, so your ds learns the signals for 'time to sleep'. You probably already do bath and then to a darkened room - are you reading a bedtime story yet? It's a good idea, even at this age.
Once that is all established for a few days, then your ds needs to learn how to put himself to sleep. My dd2 moved out of 'needing to be held to fall asleep' to 'being held is too stimulating for me to sleep, but I don't know how to fall asleep any other way' at a similar age. I suggest you do the bedtime routine, perhaps dress him in something slightly (only very slightly!) restrictive, like a sleeping bag, to recreate the sense of being held. Then put him down and sit beside the cot. He will cry, because he'll be tired and frustrated (but he won't be scared or traumatised, because you are nearby). You can pat his back, stroke his hair, hold his hand, but don't make eye contact, talk or pick him up.
Eventually he will fall asleep. You and he will be exhausted, but if you keep it up it will work.
I did this with dd1, following the advice of sleep expert Andrea Grace (she has a website with lots of advice on it - worth taking a look). She told me it would take four nights. We had one hour of crying on day 1, 15 minutes crying day 2, slept through the night day 3.