Keep relations with him, but at the same time do not condone what he is doing.

The late Ayatollah Dastaghayb Shirazi wrote in his book Greater Sins: “If Sileh Rahmi towards a Kafir (disbelieving) relative, in some way, strengthens his conviction towards his own religious views; or if Sileh-Rahem towards a sinful relative provides him with opportunity and encouragement in his unlawful ways, then this kind of Sileh Rahmi is forbidden.

In fact, if Qat-e-Rahem induces a disbeliever to introspect and reconsider his disbelief, then, Qat-e-Rahmi is obligatory on us. In the same way Qat-e-Rahem is obligatory if it discourages or dissuades a relative in his sinful ways.”