I am in no position to really advise you on such sensitive subjects, however from the limited amount of information you posted you mentioned that this boy goes out with non jewish girls, yet you are for some reason convinced that you befriending him would draw him away from those girls and closer to yiddishkeit.
now who says that you wont be drawn closer to his life, for me it appears that the risks outweight the benefits.
In fact being between people, its more likely that you will be pulled into his world then the other way around.