A different reason to cry

My little boy has just fallen asleep in his cot at last - it's taken well over an hour, and tears from him and tears from me.
As planned, we spent nearly a week of "introductions" until the big day on Friday when we brought him home, with it gradually dawning on us that not only was he about to spend the night with us, he was actually about to spend the next 16+ years with us.
I worried that in his new surroundings he may not sleep well. We brought the mattress and bedding, unwashed, from his foster home and put it in his cot here. We followed his evening routine to the letter, though of course his bath was our bath, not his usual, his surroundings entirely different. He had had plenty of time to play here, to eat here, to explore; he'd had naps here and seemed relaxed and 'at home' - but of course sleeping overnight was going to be the biggie.
We congratulated ourselves on an uneventful first night. I sang him to sleep as he lay on my tummy, his head on my chest. It was like a dream. He slept, just stirring with a whimper every hour or so. Because I sleep lightly I got up to check every time, covered him again with his blanket, but he didn't wake up till morning.
Second night, same thing.
Last night, I don't know quite what happened but he just seemed unable to relax physically. He showed every sign of wanting to sleep, he yawned, rubbed his eyes, but even when he did fall asleep he would waken himself by crying loudly in his sleep, still in my arms. Eventually he fell asleep in R's arms, we put him in his cot and he slept unusually peacefully all night.
Tonight, hoping to avoid the pattern from last night, R offered to put him down. Nope, Theo apparently just kept coming to the top stair gate and calling 'mama' until R gave up. So I tried. Pretty much everything.
I sang to him.
I rocked him.
I talked to him.
I undressed him and me and rocked him skin-to-skin.
I put him in his cot and stayed with him.
I put him in his cot and left him, though he cried. (Not recommended. This is the bit that made me cry. I cannot listen to a baby crying for me, when I could go to him. How do people do this?)
Eventually I put him in his cot and spoke firmly to him as he tried to play 'boo' with me, using his topsheet. I said "Goodnight, darling, see you in the morning" and left the room.
(He is so gorgeous). He fell asleep that time. But I feel that I don't know what I am doing.

R has 2 weeks paternity, and doesn't go back to work until 19 May, but I wonder what it will be like when he does go back. I am so tired.

He is, however, in spite of the above, the easiest, loveliest, most adorable child you could imagine.
He smiles and giggles and (mostly) eats anything. He dances to any music that comes on the radio, he looks like an angel. He is SO bright and learns so quickly.
We laugh that we fed him asparagus risotto.
He came to us with a collection of ghastly plastic toys with batteries, flashing lights and american accents (no offence, but we don't live in America). We are introducing him to nice middle-class wooden toys, and giving him loads of one-to-one.
Sometimes we play him classical music. He hears Pink Floyd and David Bowie. (Kooks - great song for our situation - look up the lyrics on google!)

I think I am doing this all wrong. I think I am trying too hard, and wearing us both out.

Please don't tell me to leave him to cry on his own in a room. I can't bear to think I would do that. I didn't wait all this time to become a mother to leave a baby to cry with no comfort and no love.

Very disjointed post.
I am in love with this child, he is completely incredible, he is more beautiful and clever and adorable than I would ever have imagined. But it is not a bed of roses. Who knew? (!)

Silly me.