@Entity
@Table(name = "player")
public class Player extends PersistableObjectImpl {
...
  @GwtTransient
  @JsonIgnore
  @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.friendOf", orphanRemoval = true)
  private Set<Friend> friends = new HashSet<>();

  @GwtTransient
  @JsonIgnore
  @Column(name = "fiends_of")
  @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.friend", orphanRemoval = true)
  private Set<Friend> friendOf = new HashSet<>();
...
}

@Entity
@Table(name = "friend", uniqueConstraints = {
    @UniqueConstraint(columnNames = {"friend_id", "friend_of_id"})
})
@AssociationOverrides({
    @AssociationOverride(name = "pk.friend", joinColumns = @JoinColumn(name = "friend_id", insertable = false, updatable = false)),
    @AssociationOverride(name = "pk.friendOf", joinColumns = @JoinColumn(name = "friend_of_id", insertable = false, updatable = false))})
public class Friend implements BasePersistableObject {

  @Id
  @GeneratedValue(strategy = GenerationType.TABLE)
  private Long id;

  @EmbeddedId
  private FriendId pk = new FriendId();
  private boolean favorite;
...
}

@Embeddable
public class FriendId implements Serializable {

  @ManyToOne(fetch = FetchType.EAGER)
  private Player friend;
  @ManyToOne(fetch = FetchType.EAGER)
  private Player friendOf;
...
}