We kept our 2-year old at home until about three months ago, when we were left in a situation needing day care. Our son cried for about 2 weeks because he had never been anywhere but home. Plus, he's an only child right now, so the whole situation was very foreign to him. And you're right, it is heartbreaking to leave them crying. But our sitter assured me that he'd only cry for a few minutes and then he'd start playing. I wondered the same thing...is she telling me the truth? I had to accept that she was telling me the truth because we trusted her enough to leave our son in her care, so I decided to try not to think negative thoughts.
Can you call often to check up on him? For the first month or so, I used to call every hour and his sitter was very patient with me calling so often. Now, he walks right in. He even gets excited when we're walking to the door on some days. Your son will adjust. But, he'll probably still have his moments. Today was the first time that my son cried after me. He kept wanting to hug and kiss me and I had to put him down. It was hard to walk away, but I called her as soon as I got to work and she told me he was just fine. ...It's probably actually more difficult for us than it is for them. =)
Good Luck with everything. Hope it works out!