Check if value exists in a column and overwrite if yes, add a new row after last if not

I'm relatively new to VBA coding and would appreciate any help and guidance.

I'm trying to compare values in column “A” in on 2 different worksheets - source and destination - and if values match - overwrite the entire row in the destination, if a value doesn't exist then I would like the macro to add a new row after last row on the destination sheet with the row of data from the source sheet, corresponding to the cell that was not found. The code works perfectly fine for overwriting the row, but I'm really stuck with adding a new row. I tried putting an Else inside the loop, and it's adding a new row, but when I run macro again it add that same row again after last row instead of overwriting. What am I doing wrong?

Code:

    Dim source, desination As Worksheet
    Dim lastrow, lastrow2 As Long
    Set source = Sheets("Sheet2")
    Set destination = Sheets("Sheet1")
    lastrow = source.Cells(Rows.Count, 1).End(xlUp).Row
    lastrow2 = destination.Cells(Rows.Count, 1).End(xlUp).Row
     For j = 2 To lastrow
        For i = 2 To lastrow2
          If Trim(source.Cells(j, 1).Value2) = vbNullString Then Exit For
          If destination.Cells(i, 1).Value = source.Cells(j, 1).Value Then
             destination.Range("A"& i, "O"& i).Value = source.Range("A"& j, "O"& j).Value
          Else
             destination.Range("A"& lastrow2 + 1, "O"& lastrow2 + 1).Value = source.Range("A"&  j,"O"& j).Value
          End If
        Next
     Next