Hia,
Yes your boyfriend will be able to stay during the day with you. Mine stayed all day with me. I was a day case and he was there from start to finish.
If your staying overnight they usually request that they leave around 10pm and if you want them to stay they can (but this needs to be booked with the hospital and it changes from place to place) there is also a fee for them to stay.
Dont worry too much it will be over with before you know it!