This is funny. Since you trust your friend, why not send directly to his wallet and he also send directly to your wallet and after that you guys can send it back to one another.
Of course, I just don't understand what he wants. If he and his friend trust each other, they can make transactions between them, but the transactions he proposes to make are a bit strange. Using an intermediary, which would have to be a trusted escrow, otherwise there is a risk of losing the money, is usually when there is not enough trust between the two parties.
You are right if two people have a good relationship and there is trust, their relationship will not be destroyed if they transact. Therefore, in terms of relationship, transactions must be done very carefully so that their relationship is not damaged due to this transaction. From that point of view, he can trade, but before trading, he needs to have enough knowledge about Bitcoin so that he does not trade in the wrong place, since the transaction will be done on borrowed money, so he has to make the right decision. If he invests in a wrong place, he may face losses, so he should invest carefully.