Separation Anxiety

My son is 1.5 years old and has now started screaming at nap time and bed time. When i say goodnight and start heading towards the door, he will immediately start crying and get out of bed. He will scream and cry at the door while holding his blankie and will not stop until i come back. This just started a couple days ago. I have laid in bed with him until he falls asleep and then sneak out but I can’t keep doing that as i don’t want it to become a habit. Plus, if he wakes up as i leave he will scream and cry.