Before studying abroad I had a really hard time deciding where to go. My roommate and I were both looking into it and decided why not go together? So we narrowed down our choices and Florence, Italy became our new home for the summer. Not everyone chooses to study with someone they know, but I am glad I did. It made the transition from American life to Italian life a little easier and a little more comfortable than some of my new friends. You always have a travel buddy and someone to grab a quick meal with (and to lend you a phone if yours gets stolen, like mine did).
However, if you are doing this I recommend that you schedule separate classes. We did half and half. One class together, and the other separate. It was a nice time to get away from one another and stop breathing the same air at all times. Studying with someone that you know does not prevent you from meeting new people and making new friends, you just have to be sure to put yourself out there. Overall, I would definitely come back with my friend and do it all the same.