A good nursery will not allow you to stay with your child. I was a nursery teacher for years and dealt with many children with separation anxiety and trust me when I say that the mothers are the ones who make it more difficult. He will cry every day until he is settled in. The secret is to leave him only for a short period of time (1 hour) every day until he realizes you come back for him every time. Then you start increasing those periods. If you are there with him, separation anxiety will worsen. Once he gets used to the idea that you come back to fetch him every time you will see a huge difference. Be strong and do it for your child. If you need any further help just pm me.