In India, there is no law that prohibits a Christian and a Muslim from being in a relationship. Interfaith relationships are not illegal, and individuals are free to choose their own partners. However, it is important to note that cultural and societal attitudes towards interfaith relationships can vary, and in some communities, such relationships may be met with disapproval or even hostility.
It is always important for any individual to be aware of and respectful of the cultural and societal norms of the community in which they live, and to be mindful of any potential consequences that may arise from their actions.
It is also important to consider that if the couple plans to get married, they may face some legal challenges as India has a personal laws system which means that different religious communities have their own laws that govern marriage and divorce. Therefore, interfaith marriages can be complicated when it comes to issues like inheritance, property rights, and custody of children.