echo two variables like the paste command is not working

Shell Programming and Scripting
1

Dear all,
I have two files like this

file1
A B
C D
E F

file2
1,2
3,4
5,6

I want this output
output_expected

A B 1,2
C D 3,4
E F 5,6

So, I did

first=`cat file1`
second=`cat file2`
FILE="$first"'\t'"$second"
echo -e "$FILE"

However, the output retrieved is
output_observed

A B
C D
E F    1,2
2,3
3,4

I know that the paste is better, but I have thousand of files to be joined and the script that I wrote is into a loop for.

I had the output_expected in a file that I created to test the script, but in the real case I just had the output_observed.

Could somebody explain what is happening? Is it absent some feature in my files?

Regards.

2 
$ paste file1 file2
A B     1,2
C D     3,4
E F     5,6
3

Thanks Cabrao, however, I have thousand of couple of files to be joined and to do a paste for all of them is not so feasible. The that I wrote is into a loop for.

4 
pr -m -t file1 file2