If you really care about your friend better to tell him everything, and teach them how to play in the market. Im not saying that you idea is illegal, its legal as long as you are committed but again teaching him about cryptocurrency is the best thing that you can do, let him enjoy the cryptomarket.
I agree mate, the OP should teach his friend on how to play in the market it feels better when there is someone who is willing to learned about crypto and you are the one who teaches him. Yes,it in not illegal but it is much a good idea if your friend will not rely on you someday.