var 
  xChr, 
  xRow, 
  xCol: LongInt;
...

xRow := SendMessage(Memo1.Handle, EM_LINEFROMCHAR, Memo1.SelStart, 0);
xChr := SendMessage(Memo1.Handle, EM_LINEINDEX, Zeile, 0);
xCol := Memo1.SelStart - xChr + 1;