I went through this with my daughter. She constantly kept coming into our bedroom. I just ignored it at first , thought if i made a fuss she would just keep coming in. It worked for awhile until she started it up again.
I bought some fairy lights and put them around her curtains and keep her door wide open. The fairy lgihts are turned off as soon as she has fallen asleep but with her door wide open and ours she says thats better for her.
Do you close both of your doors? Maybe try opening them and show him this and that you will be only there but there is no need to sleep with mummy and daddy as you are close by. Hasnt failed since, she seems much more calmer and even runs to her bed knowing that our door is open next to hers!
Good Luck i know how fustrating it is and with the back ache!!!
