Relax, it is not impossible, but it's not going to be easy, either. He will cry- I don't mean let him cry it out, as they say. But he will cry some, but if you don't get him out of your bed now, when you try later he is going to cry more... so if you go through a few days of misery now you'll save a lot later.
There are a lot of things you can do. Of course, you can just let him cry, and go in and check on him periodically, but I don't like that and a lot of moms can't handle it. You can also try the Baby Whisperer method- for more in depth I recommend the book, but basically you train him to sleep on his own without letting him cry- start out by laying him in his crib when he is calm and sleepy and starting to walk out, but the second he cries (really cries, not fuss or other noises) you go back and comfort him, first just by patting him or leaning way over the crib to put your arms around him and then if that doesn't won't work picking him up. Then lay him back down/ move away the minute he stops again. Repeat this until you can get out of the room and shut the door without him crying- be prepared, this method, while there are less tears, is much more work and takes more time. You may have to pick him up and lay him back down up to 30 times (or more in some cases), so be prepared not to sleep much the first few nights. But eventually he will learn to fall asleep on his own- you just have to realize that, so far, you have taught him to sleep on you or with you. He'll have to relearn on his own. But if you are patient and determined it WILL work- usually in no longer than 3 days. And be prepared for him to eat less at night once he learns. Once he is able to put himself back to sleep he won't need you as much at night- I would be willing to bet that he is nursing a lot at night because he does it to get back to sleep. And speaking of which, it's not a good idea for him to nurse in order to fall asleep, because it will impeed the process (it will be harder for him to learn to fall asleep himself).
I don't know that co-sleeping is good for a family. I think it's helpful in the very very early months (up to 3 months), and I respect the cultural differences of others who do it because it is part of their culture. However, it is difficult for two parents who grew up with their own space and who have had their own space (shared with their spouse) and had freedom to be intimate at will to give that up and for one of them to not resent it. Neither of them may say so, but one of them probably does and feels guilty about it. The parents tend to loose sleep, or they don't even sleep together in the same bed. The entire household becomes very child centered, with all of the needs (of which sleep is one of the most important) of the parents getting pushed to the side. Personally I think that balance is healthier for a family. Balance in which everyone has enough alone time and together time, and in which everyone's needs are met for the most part. Co-sleeping is one of those things that sounds really great in theory, but few parents think it through to conclusion (like "am I still going to want my child in bed with me when he's 5?") However, I am getting preachy and rambly and that's not my point.
Last, at the risk of sounding motherly (but really, I can't help it), take this lesson to heart- it's one I had to learn the hard way too. When making decisions about your child in the future (like you did when you kept him in your bed past 3 months) think it through to conclusion- will it be a hard habit to break? Does this work for my family? Etc. I know, it's hard though. As I said, I made the same mistake and many others- it's like you're in survival mode those first few months. Upcoming possible trials for you- I don't know how you feel about breast feeding, but emotionally it is easier to wean a child around their first birthday than later (same as with bottles). Any longer and it becomes an emotional crutch for the child. I respect the whole bonding thing, but by this age there are lots of other ways to bond with your child, and also by this age they have moved passed the developmental stage when they are bonding and developing trust in their primary caregiver into the stage when they should be developing autonomy. Same with binkies, although it helps to loose only one at a time.
