Different religions in relationship

I am catholic and always have been... Tata is a faithful christian.His brother and sister scholarship in a medical school was sponsored by christian worship.I have been always wondering what other people thoughts and opinions are when it comes to religion in a relationships. Tata and I is more than a year but religion is not an issue to us. When I bring him to go with us in catholic church I haven't heard complain or refusal.But, when he invite me to go with him in christian house of worship I turn down.Tata said its better that we have only one religion someday, but I stand my decision that I will remain catholic.I will be willing to be baptize in christian but doesn't mean I will leave for being a catholic.let me ask;Is there a dual religion?could it be? I still don't know the answer but that is only an arrangement.I know tata will not forced me at first he really know who am I.