Hi E., I co~slept with my son until about a month or so ago (he's 31 months, or 2 1/2) because he refused to go to sleep by himself. The way it happened was almost on accident, but it worked and I kept it going. I was staying with a family member and she and I were busy doing other things at bedtime. So we put my son on the couch with his bear, a pillow, blanket and watching a movie. He's very stubborn and stayed awake during the whole movie, but afterwards he kind of fussed some and asked me to lay down with him. I told him that I couldn't because God Mimi needed my help and he layed there and watched and listened to us until he went to sleep. I think him being able to see me helped some. When we came back home, I put him in my bed (where he's used to sleeping) with my pillow, our blankets and his bear and lamb. I gave him a hug and a kiss and told him it was night night time and that I loved him and left the room leaving the door open just a crack with the light in the room on (he's afraid of the dark). The first few nights he cried for a long time and eventually he quieted down and fell asleep. It took about a week and a half for him to get that I wasn't going to lay down with him anymore and he doesn't usually fight me to go to bed anymore. It helps if you keep his usual routine except for laying down with him (ie. reading to him, bottle, etc.). If you can help it, DON'T check on him at all, or if you need to, only once or twice. When I did that, my son got upset all over again and now that I don't, he goes to sleep much faster. We're working on getting him used to going to sleep in his own bed now that he can go to sleep by himself. It's going to take some time, but don't lose hope, it WILL happen. :)
I hope this has helped!