Is it inappropriate for a Catholic to date a Mormon who will be leaving for a mission?
There is nothing “wrong” with it. Though most members discurage serious relationships to form until after the mission. Also, there is the danger that he might become distracted and not go on a mission at all. As for the non-catholic thing, it’s a personal choice who to date, but members are encouraged to marry within the faith so that they can be sealed in the temple and have an eternal marriage that will not end at death. This is a very strong idea within the church. But on the flip side there are alot of part member families in our church, and it will not keep him from being considered an active member of good standing in the church.