I have an unfaithful friend, and I want to distance myself from him for my personal benefit, despite my sincerity towards him.

All praise is due to Allah. The Shari'ah has established a criterion for choosing a friend, which is religiosity and righteousness. A good companion is like the bearer of musk: he will either give you some, or you will buy some from him, or you will find a pleasant scent. A bad companion is like the blower of bellows: he will either burn your clothes or you will find a foul odor. If your friend is righteous and helps you in good deeds, then continue your friendship with him and advise him if he makes a mistake. If he is a bad companion who negatively affects your religion and morals, then advise him; if he does not mend his ways, then cut off his companionship.