Hi M.,
I had the same problem for my son, we co-slept for a few months, and then got him to sleep in the crib, but he would never go to bed by himself, I had to rock him to sleep and try not to disturb him when I laid him down, if I did he was up for another couple hours until finally around midnight he would fall asleep exhausted.
I ended up using ideas from the book "Good Night, Sleep Tight" by Kim West. It is a method from "the Sleep Lady" who has this great method to get your kids to fall asleep on their own and sleep all night long. It took us about a week and a half, and the crying went from 45 minutes to 15 minutes within 3 days, and after that it was just getting him to sleep.
Her method is basically, comfort them from next to the crib but do not take them out, until they fall asleep. stay next to the crib for a few days until they fall asleep faster, then gradually move away from the crib when you comfort (using your voice) until you are in the doorway, and by then they should be falling asleep with no problems. It is much easier if you have a routine before putting them to bed, like a bath and some stories.
Good Luck!