L.P.
Now that a pattern has started it needs to be broken. Like creating the pattern took time, so will breaking it. I would suggest finding a way to make staying in his own bed fun, like special story time at bed that is only done when he sleeps in his own bed. Use your imagination, think about what your child's interest are and create a new bedtime ritual that revoles around him staying in the bed. Consistancy from both you and your husband on what you decide is the key!! One can't try to change things while the other gives in. The more creative and special you make the transition, the less your child will see it as a negiative change and will be more apt to not only follow, but enjoy.
Good Luck
L. P