I got a workaround myself:
    'G = Maximum amount of characters for width of comment cell
    G = 100
    'CommentX
    If THISWB.Sheets("Source").Cells(i, CommentColumn).Value = "" Then
        CommentX = ""
     Else
        CommentArray = Split(THISWB.Sheets("Source").Cells(i, CommentColumn).Value, Chr(10)) 'splits on alt + enter
        DeliverableComment = "Available"
    End If
                        If CommentX <> "" Then
                            'this loops for each newline in a cell (alt+enter in cell)
                            For CommentPart = 0 To UBound(CommentArray)
                            'format comment to max G characters long
                                LASTSPACE = 0
                                LASTSPACE2 = 0
                                    If Len(CommentArray(CommentPart)) > G Then
                                        'find last space in G length character string to make sure the line ends with a whole word and the new line starts with a whole word
                                        Do Until LASTSPACE2 >= Len(CommentArray(CommentPart))
                                            If CommentPart = 0 And LASTSPACE2 = 0 And LASTSPACE = 0 Then
                                                LASTSPACE = WorksheetFunction.Find("þ", WorksheetFunction.Substitute(Left(CommentArray(CommentPart), G), " ", "þ", (Len(Left(CommentArray(CommentPart), G)) - Len(WorksheetFunction.Substitute(Left(CommentArray(CommentPart), G), " ", "")))))
                                                ActiveCell.AddComment Left(CommentArray(CommentPart), LASTSPACE)
                                            Else
                                                If LASTSPACE2 = 0 Then
                                                   LASTSPACE = WorksheetFunction.Find("þ", WorksheetFunction.Substitute(Left(CommentArray(CommentPart), G), " ", "þ", (Len(Left(CommentArray(CommentPart), G)) - Len(WorksheetFunction.Substitute(Left(CommentArray(CommentPart), G), " ", "")))))
                                                   ActiveCell.Comment.Text Text:=ActiveCell.Comment.Text & vbNewLine & Left(CommentArray(CommentPart), LASTSPACE)
                                                Else
                                                   If Len(Mid(CommentArray(CommentPart), LASTSPACE2)) < G Then
                                                       LASTSPACE = Len(Mid(CommentArray(CommentPart), LASTSPACE2))
                                                       ActiveCell.Comment.Text Text:=ActiveCell.Comment.Text & vbNewLine & Mid(CommentArray(CommentPart), LASTSPACE2 - 1, LASTSPACE)
                                                   Else
                                                       LASTSPACE = WorksheetFunction.Find("þ", WorksheetFunction.Substitute(Mid(CommentArray(CommentPart), LASTSPACE2, G), " ", "þ", (Len(Mid(CommentArray(CommentPart), LASTSPACE2, G)) - Len(WorksheetFunction.Substitute(Mid(CommentArray(CommentPart), LASTSPACE2, G), " ", "")))))
                                                       ActiveCell.Comment.Text Text:=ActiveCell.Comment.Text & vbNewLine & Mid(CommentArray(CommentPart), LASTSPACE2 - 1, LASTSPACE)
                                                   End If
                                                End If
                                            End If
                                            LASTSPACE2 = LASTSPACE + LASTSPACE2 + 1
                                        Loop
                                    Else
                                        If CommentPart = 0 And LASTSPACE2 = 0 And LASTSPACE = 0 Then
                                          ActiveCell.AddComment CommentArray(CommentPart)
                                        Else
                                          ActiveCell.Comment.Text Text:=ActiveCell.Comment.Text & vbNewLine & CommentArray(CommentPart)
                                        End If
                                    End If
                            Next CommentPart
                            ActiveCell.Comment.Shape.TextFrame.AutoSize = True
                        End If
Feel free to thank me. Works like a charm to me and the autosize function also works!