I think that there's something that sometimes moms tend to forget when it comes to their children, and that is it is the parent who is in control in a parent/child relationship, not the child. I think that overall, it is the act of forgetting this very important concept that gets mothers and fathers into binds where there kids are out of control in one area, or even several areas.
You have to remember that a child crying is NOT the same as when you or another adult cries. We cry because we're sad, or happy, or hurting. I realize that a child cries when they get hurt too, but you understand, I'm sure, that most of the reasons a child cries are not the same ones that will make them cry when they're older. A child doesn't really understand yet how to control their feelings. They haven't learned yet the whole concept of keeping their composure. They just know that they want to cry, and so they do. They do it for attention, they do it to express their anger and other feelings, and lastly, they do it because they know mommy will cave! Now,that being said, you have to remember that it just plain isn't up to the child whether he/she sleeps with you or not. It's up to you. You are the mother and you are the one in control. Now, I don't agree with the whole sleeping with your child thing, but that's because I believe this severely compromises the child's early development of independency skills. Just keep in mind though that since you have allowed the child to sleep with you, you have made yourself his "security blanket". He now feels probably scared, and at the very least, very alone in his own room. So, try to replace yourself with something, so to speak. Let him sleep with your pillow, so he can smell you while he's trying to fall asleep. You can even pull a blanket off of your own bed for him to sleep with. Also, buy a monitor that also has a walkie talkie on it, or just buy a walkie talkie. YOu can show him that if he ever needs you, he can speak into the monitor and you'll be able to hear him. You could also speak back if you'd like. Now, you'll also have to break him of constantly getting up throughout the night and coming to your room. Just pick him up or grab him by the hand, walk him quietly to his room, and put him back into his bed. Don't talk to him while you do it because that would be "showing him attention" Believe me, a few nights of consistently doing this, will make him realize that there's no use in trying anymore. Kids are so smart and if you cave just one time by letting him crawl in bed with you, or you crawling in bed with him, they will remember and it will ALWAYS be worth trying to them, because they will know that you have a breaking point in there somewhere. Do not sleep with him either, it's just trading one problem for another. Kids need to learn to be independent. They need to learn to fall asleep by themselves, without mommy walking or rocking them, they need to learn how to fall back asleep by themselves when they wake up at night, and they can only learn these very important values if we as mothers give them the opportunity to do so. If we keep running in their rooms everytime they cry, and allowing them to sleep with us, then WE become "what calms them down". In my humble opinion, this isn't the healthiest way for a 2, 3, 4, 5, or older child to learn independence.
Hang in there, it will take a good 3 days, but once it's done, it's such a remarkable relief and you'll be so very proud of your child...and yourself!