I Need To know something about GTA4?

I just started playing but I'm to the part when Dimitri Burns Down ur house and Cab place. I know Michelle is like an uder cover cop or something but when does she tell you and u don't see here any more. Also are you allowed to date other girls when ur with Michelle or do u have to wait till u stop seein here. Cause I just finished the mission when u get the sniper rifle. But I heard your allowed to date other girls when ur done with out of the closet mission. Some one help me plzzzz