Depends on how you look at it, but yeah. I was going out with my first girlfriend, when I went to a camp trip with my girlfriend's best friend (who I also happened to like.) I fully intended for nothing to happen, but we sat around and talked a lot since we didn't know anyone else. It was never said, but we really liked each other, and I actually leaned over to kiss her at one point, but she stopped me and told me she couldn't do that to her friend. >.<
Needless to say I broke up with my girlfriend when I got back home, but I didn't get the best friend either. I just simply lost. XD
Nothing so serious as to be sexual though. So whatever, take it for what it is worth.