well at least you are in the process now, before baby #2 comes home.
It takes time, each kid being different. He just wants to make sure you are there and he is safe. He will transition in time and feel better about it. Give him time, but not a hardcore deadline. Some kids don't do well with the feeling they are being 'rushed.'
Let him have loveys in bed with him, a flashlight he can keep in bed with him, a sippy cup of water in bed with him, all the pillows he wants. That is what our daughter LOVED to do... she called it 'making her nest.' And she would make things all cozy and she had a whole 'routine' about getting her bed 'ready' and what to put in it, before she would sleep.
Try to engender a routine that he can do, prior to lying down in his bed. His "own" thing.
At about 2 years old... they change a lot and we put changes on them too, at this age. Beds being one of them, and they get ousted from co-sleeping & having a new baby sibling. So, they will need to adjust. AND at this age, kids start to have night-time fears or fears of the dark etc. Its normal.
My kids and I co-slept too. I was like that too, with my kids, and I did just the SAME as you to put my girl to sleep. Its okay. They grow out of it.
BUT... for us, we also have a floor futon in our room... where the kids can come in and sleep on IF they need too. It doesn't bother us. It works out for us. Its a happy medium. A sort of 'transition' thing. We are not the types to barricade our kids in their rooms with gates etc., so this floor futon is our solution and even when I had my 2nd child.
Just see what works for you and him. He will get it. Just not yet. But I think what he is going through is normal. And even at this age, its a form of 'separation anxiety.'
Or what you can do when he calls for you every time he wakes is: don't go in right away. Just wait... make like you don't hear him and are sleeping. Wait. And he may go back to sleep on his own. That is what I did sometimes. Or tell him... "in a minute..." then just wait. Don't go quickly.. .and in the process of him "waiting" for you he may fall back asleep again. That is how my son is. But for my daughter, well she'd literally wait and count the minutes. Ha, ha. So that method didn't work.
Or maybe give him a t-shirt of yours... one that is not freshly washed and smells like you and is all cozy. A t-shirt you wear all the time, and let him sleep with it. My daughter, being the way she is... LOVES to sleep my ol' ratty t-shirt. And she hugs it as she sleeps. It makes her feel safe and comforted. And explain to your son that he can hug that...
All the best,
Susan