EntityFramework and relationtionships - asp.net-mvc

Question

Imagine the person Ted. Ted use bulletin board. He can post ads and subscribe to ads (imagine ad is some event.. teaching lessons for example). So as you guessed we have two objects: Advert and User (Ted). One user posts different adverts and in the other hand one user subscribes for different adverts. So we have two types of relationships: One-to-Many (Ted to his adverts) and Many-to-Many (Advert to subscribers - subscriber to adverts).
So the Models looks like:
[Table("Users")]
public class User
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
[Display(Name="Login")]
[Required(ErrorMessage = "Enter the login.")]
public string Name { get; set; }
[Required(ErrorMessage = "Select the city.")]
public int CityId { get; set; }
public City City { get; set; }
public int? SpecialityId { get; set; }
public Speciality Speciality { get; set; }
public virtual ICollection<Advert> Adverts { get; set; }
public virtual ICollection<Advert> SubscribedOnAdverts { get; set; }
public User()
{
Adverts = new List<Advert>();
SubscribedOnAdverts = new List<Advert>();
}
}
And Advert:
public class Advert
{
public int Id { get; set; }
[Required(ErrorMessage = "Enter your ad title")]
public string Title { get; set; }
[Required(ErrorMessage = "Enter your ad text")]
[Display(Name="Advert text")]
public string Description { get; set; }
public int? Price { get; set; }
[DisplayName("Owner")]
[Required(ErrorMessage = "Select ad owner")]
public int UserId { get; set; }
public User User { get; set; }
[DisplayName("Speciality")]
[Required(ErrorMessage = "Enter the speciality")]
public int SpecialityId { get; set; }
public Speciality Speciality { get; set; }
[Column(TypeName = "DateTime2")]
public DateTime publishTime { get; set; }
public virtual ICollection<User> SubscribedUsers { get; set; }
public Advert() {
publishTime = DateTime.Now;
SubscribedUsers = new List<User>();
}
}
Let's look at the User model: you can see the same type of props: Adverts, SubscripedOnAdverts. If we delete SubscribedOnAdverts property from the User model and SubscribedUsers from the Advert model, following code will perfom correct:
IEnumerable<Advert> userAdverts = db.Users.Where(usr => usr.Id == id).FirstOrDefault().Adverts;
It will return adverts this user posted.
But with the above properies (SubscribedOnAdverts in User model, SubscribedUsers in Advert model) it will return empty Collection.
Normal:
With problem:
I can guess why it happens. But i don't know how to fix this issue and save the relationships.