My son won't sleep in his crib?

My son is 18 months old and i'm now trying to get him to sleep in his crib. Yes I know I shouldn't have let him sleep with me to begin with but because he had acid reflux and he was colicky when he was small it was so hard to even put him down that I was feeling fatigue all the time and his pediatrician advised me I need to be healthy and in functional condition to take care of him so if he will sleep when with me do it. Yes I let it go on too long and i've been criticized enough for it and I fully acknowledge my wrong. My question is how do I get him to sleep in his crib?? I tried last night but he cried bloody murder for and hour and it broke my heart and couldn't let it go on any longer. I even laid beside the crib and tried leaving the room and still he sobbed. It hurt me to see him so upset because he's such a happy little guy and rarely cries. Any advice on how to get him to sleep in his crib I greatly appreciate. Thank you to all who respond.