Help! My awesome sleeper has been waking and refusing to fall back asleep in his own bed.

DS is 3 years old and has not fully transitioned out of his crib. He will sometimes sleep in his big boy bed, but 8 times out of 10 prefers the crib. He has always been a great sleeper and never much into co-sleeping (only when sick) but a few nights ago he woke up and my DH went to check on him. DS asked for me so DH brought him into our bed. Well…every night since he has woken up in the middle of the night and been inconsolable until we bring him into our bed. At first I tried to fight it, but now it’s just easier to give in and I fear that we are starting a bad habit. Most LO’s transition out of co-sleeping at this age, whereas mine is regressing backwards!

Part of me hopes it’s just a phase. DD is 4 months old and sleeps in our room still so maybe he’s feeling left out? Sibling anxiety? The problem with them both being in the room is if I ever have to feed DD in the middle of the night it usually wakes him. But then if he’s screaming he wakes up the whole house.

Anyone experience this or have any tips on how to try to convince a three year old in the middle of the night to fall back to sleep in his own bed??