According to WTBS it is an impossible connection. You have probably read a lot of arguments why this kind of marriage “is not according to scripture”. And in fact many other religions are teaching accordingly.
But the question is how deep is the persons personal believes. And above all does he/she accept all the dogma’s that their religious leaders tell them? One person can be named Christian because he/she is just borne in a Christian country. In fact he consider himself atheistic or deistic (don´t know or just don’t want to take a stand). Some atheist goes to church because they like the music in their church. Some consider themselves JW:s because they meet their friends in the KH, every week, but they would never dream of take a part of the preaching work.
If two persons with what you call “liberal” thinking want to marry I don’t think that whatever the differences are in their “labeled religion” could be a problem. But if one of them turns (by his or hers believes) to a more fundamental believing, and think that he/she must follow the official rules more strictly, then this marriage can start to creak. The weak “believers” will have a tendency to listen to their mate rather than their pastor or elder, pope or clergyman.
Hoping that your spouse belongs to that category.
Bugbear