my 4 YO won't sleep in his own room

HELP! My fiancé and I are so sleep deprived and not because of our 5 month old! It's our 4 YO. He was always good with sleeping in his own bed, wake up at 4am and jump into ours. Well, now with a new born, he can't just jump in bed with us. We are trying to teach him to sleep throughout the night. Waking up every night and walking him back to bed, getting him in bed and he WONT sleep unless we cuddle him and he falls back asleep. So he's been comforted to know that one of us at all time will sleep with him. Well this is the bad habit we're trying to break and nothing has worked. Suggestions? Tips?! Incentives are short live. He just keeps repeating "I don't wanna sleep by myself". As we sleep WITH him, he'll wake us up and make us hold him so he'll know we won't leave his side at night.