Trying to maintain a long-distance relationship with someone at home or attempting to date someone you meet while on mission are both distractions. I'm pretty disturbed by the level of dismissiveness seen in many of the comments here. I really like this girl but, is Mormonism so toxic that I should just sever the relationship before it gets serious. Interfaith marriage is but one variety of the learning experience. I'd just like to add that unless you're happy being with her as a full believing Mormon, don't stick around in the hopes that she'll de-convert. Either way, if you have kids and you don't convert, she will divorce you and take your kids away from you and you will be shunned from her community. Marriage to the right person is wonderful. Accept yourself, and feel God accepting you, and everything else will follow. I don't know if I can do it or if I want to. And Mormons were basically encouraged to marry other mormons.
Love the man you are going to marry- warts and all he loves yours as well. But I do still largely consider us an interfaith couple. We started dating 16 years ago, and both resigned from the church earlier this year. If she is motivated enough to want to go on a mission, she will likely not settle for having a second class "eternal companion" you who is a convert or one who cannot be sealed to her for eternity. Mormons are very strict about avoiding sex outside of marriage.