I so get that, and Darcy was way older when I had to leave her. I never goes away but it does become easier. It is a hard thing you're doing. Don't beat yourself up, consentrate on the positives for him and for you.
I still hate that smell.
Like Krys says develop a relationship with the carers. The girls at our centre are wonderful and that has made it so much easier for me. They have a very similar caring 'technique' i guess you would call it, to me, so I was happy knowing it is consistent for Darcy. She too is a child of routine - so much so that on Christmas day she woke up (or was woken up I should admit) and said, "school mum?"