Import very big text file into sql. Speed problem - sql

Question

I must import a big text file into sql database.
The text file contains some 5 million of rows. :D
My pc is old ed I use vb.net, but is only for one shot.
When import started, the code read and entered 100 lines for second.
Is slowly but for one shot is not a problem.
Now, at 300.000 lines readed, it work ar 8 lines for second. :(
The goal is far away....
The strange thing is, if I start from first line and in the database have 300.000 record, the speed is fast (100 L/s) even though I check that I don't have the record.
In sql I created a cluster index.
This is the vb.net code into BackgroundWorker DoWork:
Private Sub Bw_DoWork(sender As Object, e As DoWorkEventArgs)
Dim d = DirectCast(e.Argument, BwData).Path
Dim s = DirectCast(e.Argument, BwData).Start
Dim reader As IO.StreamReader = My.Computer.FileSystem.OpenTextFileReader(d)
Dim l As String
Dim lineIndex As Integer = 0
Dim lineStart As Integer = 0
Dim part As String() = Nothing
Try
Using ctx = New ContentsDBEntities
Dim rowN = s 'Math.Max(ctx.xHamster.Count - 100, 1)
Do
l = reader.ReadLine
If l Is Nothing Then
Exit Do
End If
part = l.Split("|")
If Bw.CancellationPending Then Exit Do
If lineIndex >= rowN AndAlso part.Length >= 14 Then
If lineIndex = rowN Then
lineStart = lineIndex
startAt = Now
End If
Dim vId = part(0)
If IsNumeric(vId) Then
Dim there = (From c In ctx.xHamster Where c.VideoId = vId Select c).FirstOrDefault
If there Is Nothing Then
Dim r = New xHamster With {
.VideoId = vId,
.Url = part(1),
.Umbed_Url = part(2),
.Title = part(3),
.Duration = StringToSec(part(4)),
.dateAdded = Date.Parse(part(5)),
.Thumb = part(6),
.Channels = part(7),
.Pornstars = part(8),
.MaxResolution = part(9),
.Orientation = part(10),
.Title_RU = part(11),
.Username = part(12),
.Description = part(13)}
ctx.xHamster.Add(r)
If lineIndex Mod 100 = 0 Then
ctx.SaveChanges()
End If
End If
End If
End If
lineIndex += 1
DirectCast(sender, BackgroundWorker).ReportProgress(lineIndex, lineStart)
Loop Until l Is Nothing
reader.Close()
ctx.SaveChanges()
End Using
Catch ex As Exception
Debug.Print(ex.Message)
End Try
End Sub
Do you have a trick for me?
Why does the speed decrease?
Thank you
Luca