One of my best friends is a girl, but, there needs to be the understanding between both of you that you do not feel that the time spent together is romantic. Also, be careful on if you pray together, etc. Intense one on one personal prayer with somebody of the other gender is the most intimate thing you can do besides...because you are offering your 2 spirits, which if they are both of God, they are both perfect, they are combining and offering the prayer up to God. So that is some pretty intimate stuff. But yes, you can be best friends with somebody of the other gender, but just be careful with that when you do find somebody that you are interested in so that it doesnt look bad to either of them, or others.