You'd be surprised. I went to costa rica with 3 guys who pretty much only spoke english, and so I only spoke english with them. It would have been better if the guys I went with knew as much spanish as me, because then we could have been practicing all day everyday as we found our way around. I picked up some new stuff, but not much. It might be a good idea for both of you to focus on just one language so that you can practice together. Then, like Julie said, worry about the other language.