Well in this case, they are interchangeable, which means that you can use either of them and it will still have the same meaning. * We are just friends * We are only friends

Yes in this context they are the same , but note you can't say it the way you put it " we are just a friend " or " we are only a friend" It has to be "we are just friends OR "only friends""

"Just a friend" and "only a friend" Are basically the same thing. If someone asks you "Are you dating that person?" you can say "I am just a friend to him/her". Stuff like that ^.^ Really, both are correct, and they have the same meaning.