in VS Code I have the following file

1
2
3

a
b
c

Now I do the following steps

1. cut the lines a b c.
2. select the lines 1, 2, 3 and then go into multiple cursor mode (shift, alt I).
3. go to the end of the each number press and type a comma , and then do a paste.

The result is

1, a
b
c
2, a
b
c
3, a
b
c

but the result I wanted is

1, a
2, b
3, c