It's very common that a consultant has to leave early for various reasons. Managers usually don't take it personal.
IMHO, you may schedule a time with your manager. Tell him that you've got a new contract somewhere else. The new job could not be delayed by 2 months, therefore you have to take the new job soon. However, you'd like to make sure that there's minimum impact to your current project. You may offer to work part time on the current one, to make sure the transition goes as smooth as possible.
IMHO, you may schedule a time with your manager. Tell him that you've got a new contract somewhere else. The new job could not be delayed by 2 months, therefore you have to take the new job soon. However, you'd like to make sure that there's minimum impact to your current project. You may offer to work part time on the current one, to make sure the transition goes as smooth as possible.