You are being controlled by your son. He has way too much power here. I'm sure he would never have any friend sleep over his house because he would be humiliated for the friend to know that he slept with his mom. At his age, unless the two of you have had a co-sleeping arrangement all along, he should not be sleeping with you for a variety of reasons.
You need to have a few calm conversations with him about how and why this is going to stop-and then make it stop. If this means your having to sleep beside him in his room, on a mattress on the floor until he falls asleep, so be it. Make the commitment to spend less and less time in his room as this routine progresses. It's certainly easier for you to first get him in his room and then deal with your leaving it than to keep kicking him out of your room when he keeps coming in after you've put him to sleep (awake ) in his room.
Clearly this situation is about things other than his sleeping preference. You have to take a stand here because he can't/won't- you're the parent. If your actions cause considerable, daily emotional problems on his part, and the situation is the same or worse after two weeks, you need to seek professional psychological help to sort this out. Please take action as this situation is masking other more serious issues.