Should one who engages in foreplay of an indecent act with an unpubescent boy in a mosque leave the mosque where the sin is taking place, or should he abandon the place of sin without caring what people might say?

Avoiding such abominations is essential. If praying in a specific mosque leads to this abomination, then go to another mosque and do not mind what people say, for Allah is more deserving of awe. More important than changing the mosque is repenting from this vice and from violating the sanctity of Allah's house, for both are grave sins. The door of repentance is open for whoever repents and turns back [to Allah]. And let him frequently supplicate: "O Allah, purify my heart and protect my private parts."