Implement Cross-session Data Controller Class?

I am creating an ASP.NET application that allows users to edit and insert data that is persisted in a SQL Server database.I would like to implement a controller class that handles queries for certain entities, caches results and triggers events when data is inserted or updated.I need one of these controller classes for each entity in my data model.What I'm unsure of is how to create a singleton class of this sort that different user sessions can access.

For example,I have a Employee entity in my data model.I would like to have an EmployeeController class that handles retrieving the employees from the database, sends inserts and updates to the database,keeps a cache of all employees and triggers events when an employee is inserted or updated.Objects in other user sessions could then listen and respond to these events.

Am I on the right track?Should I be using the ASP.NET MVC framework to accomplish this?How do I instantiate these controller classes when the first user needs them and have subsequent concurrent users access the same class?

EDIT:I've been researching the idea of a controller class as an anti-pattern since @TomTom's answer.I'm not convinced one way or the other.I still need an answer to question #3 above.Let's just drop the specific idea of a controller class for now. How do I create any class that is:accessible by multiple user sessions,allows only one instance,is deleted if there are no user sessions,and triggers events that other classes can listen to.