I need to concatenate these two files (join together) using a comma, and put the result in a new file.

Here is the output:
ccusers (file1) - lli,build,mteno,clesingh,ccadmin,cmethot,jazhu,bsc hwerd,vnesher,sshkrebe,dtait,doolley,mxu,bdickins, jamyoung,gdjambov,elaakso,tpapic,cyerrado,rnakka,m sundara


tlsusers (file2) - wkint,ygoldrin,ccadmin,ggilhula,dbrodski,dchan,kfa va,sdesouza,cmcewen,aokun

I want the result be like this:
lli,build,mteno,clesingh,ccadmin,cmethot,jazhu,bsc hwerd,vnesher,sshkrebe,dtait,doolley,mxu,bdickins, jamyoung,gdjambov,elaakso,tpapic,cyerrado,rnakka,m sundara, ygoldrin,ccadmin,ggilhula,dbrodski,dchan,kfava,sde souza,cmcewen,aokun

If I use something like ("cat file1 file2 > file3") the result will be:

lli,build,mteno,clesingh,ccadmin,cmethot,jazhu,bsc hwerd,vnesher,sshkrebe,dtait,doolley,mxu,bdickins, jamyoung,gdjambov,elaakso,tpapic,cyerrado,rnakka,m sundara
wkint,ygoldrin,ccadmin,ggilhula,dbrodski,dchan,kfa va,sdesouza,cmcewen,aokun