Praise be to Allaah.
We put this question to Shaykh Muhammad ibn Saalih
al-‘Uthaymeen, may Allaah preserve him, who answered as follows:
He does not have to (cut off ties with his
non-Muslim friends), so long as they are not causing him any harm. But he
can withdraw from them gradually. He should tell them about Islam, because
if they see that he has become Muslim, they may become Muslim too. And
Allaah knows best.