Any way of avoiding co-sleeping with toddler?

My son will be 3 in November and he's been sleeping in his own room since he's 1. We used to be able to plop him down in his bed when it's bedtime and he'll put himself to sleep within minutes. Now that he's older we've removed one side of the crib to give him more freedom and now the tide has turned. Now he would refuse to go to bed and keeps trying to crawl out even though he keeps yawning and is barely able to keep his eyes open. the only way he would go to sleep is if my wife or I stay beside him until he falls asleep. Problem is when he wakes up in the middle of the night and he notices mommy or daddy isn't beside him anymore he'd start crying and yelling for us to bring him into bed with us. Is there a good way to get him to sleep alone?