I'm a huge fan of co-sleeping, but as someone else pointed out, if it's no longer working, time for a change!
I moved our son out of our bed at age 2 (husband insisted, I wanted to keep him there till he was 5). I moved our daughter at age 1 (wow husband is right, having the bed to yourself really is great). I just started nursing her to sleep on the mattress at the foot of my son's bed (he was 5 at the time). So she got used to her own bed early. It's not too late for your son.
TRANSITIONING
Give him a new room and his own twin bed (or full whatever works). Start putting him to bed there, not your bed. I would still lie with him to sleep, so it's not a huge change, but a transition.
My daughter (9) still likes me to cuddle with her before she conks out.
WHAT TO DO IF HE WAKES UP IN THE MIDDLE OF THE NIGHT AND COMES TO YOUR BED
This is easy. No words, no arguing, no debating. Walk him quietly back to his bed and crawl in with him. Both of you conk out. This makes him feel VERY safe in his bed and his room. It makes his bed the place to be. You want him to associate his bed with love and safety (and take the focus off your bed.) If he gets up due to a nightmare, he'll want to snuggle anyway. My daughter is not allowed to sleep in our bed, but if I'm too brain dead and she's too scared, I let her in. That is rare.
GETTING HIM TO SLEEP EARLIER
This is the very tricky part. My kids have always gone to bed between 8-9. I envied parents who got their kids on a 7:30 pm bedtime. Their kids wake up early.
Kids really need more sleep. It affects their behavior and learning.
7 o'clock bedtime - I wish I read this book years ago.
http://www.amazon.com/The-OClock-Bedtime-healthy-playful/...
I know a woman whose 2 daughters (9 & 8) sleep at this time (7:30-8) and they never get sick. Immune system is also made stronger by rest and a good diet.
Mary Sheedy Kurcinka wrote a great book
SLEEPLESS IN AMERICA: Is your child misbehaving or missing sleep?
http://www.amazon.com/Sleepless-America-Child-Misbehaving...
So as the parent of a 13 yr old boy who wants to stay up till 11pm and can't wake up in the morning, I beg you, fix this now while you still can. :)