P.M.
I created the same monster. It took a while, but I broke my daughter of the habit. It may cramp your bedtime routine for a while, but in the long run, it is worth it. My husband and I brought a small mattress into our room. Our daughter would fall asleep there and stayed on the mattress after a couple of night of putting her back on it in the middle of the night. After a week of her staying on the mattress, we slide it closer to the bedroom door. Each day we moved it a bit closer and a bit closer, until she was out in the hallway. We kept creeping the mattress closer to her room until it was finally in her room. She slept on that mattress on her bedroom floor for a year, then she decided to try her bed. The good news was, if she left her bed, she went to the mattress on the floor and not our bed. Just one idea! Good luck!