2-3 yr old will not go to sleep without me!

I need advice! I have a beautiful 2 (almost 3) year old boy who has never had sleep issues. He has been a wounderful sleeper since about 7 months old. And now, oohhh now. He has a bed time of 8pm and this has never changed. We are pretty strict on bed time so he has always had this consistency. Within the last 3 weeks he has been crying and following me to the stairs because he doesn't want me to leave his room. And then this week, he has been SCREAMING and crying as soon as we are finished reading his books. Now he is making himself so upset he is getting sick almost nightly. He is not calming down unless I stay in there until he falls asleep and then is coming into mom and dad rooms in the middle of the night.. Has anyone had these issues and what are some good suggestions on calming him down!?