p.s. Since a JW is admonished not to even date a non JW. How has a JW
spouse navigated things in such a way as to end up with a non JW
spouse?
One way they do it is to leave the Watchtower religion temporarily, date the non-JW, become married, and then go back to the Kingdom Hall seeking
reinstatement (this often happens when a baby is on the way, as others have mentioned). The returning JW will hear some stern talking-to from the elders, and effectively will be on probation while re-earning their status as an active, obedient witness. This is how I came to be married to a JW; my ex-wife left the Kingdom Hall before we met, and returned soon after we married.
Another way applies married couples where neither is a Witness. Then one spouse converts to the Watchtower Society, but the other. If the Un-Believing Mate loves their spouse and values the marriage, he will want to stay with his wife regardless of her religion. I use the pronouns' gender deliberately: a JW wife is supposed to be obedient and subservient to her husband, while if the husband converts to the Watchtower he is expected to exercise headship and make his wife do the right thing--i.e., go with him to every meeting at the Kingdom Hall and go with him for at least ten hours of door-to-door preaching (service) every month. He would be seen as spiritually weak if he does not convince her to do so.
Yet another way is if both once were JWs, but one of them either left the Watchtower religion (disassociated) or was kicked out (disfellowshipped). The former witness becomes a pariah, and often the subject of speculative gossip. The JW spouse and other family members are taught to limit their interaction with the former JW to essential family business. Their JW friends without family ties are expected to avoid the former witness altogether. That adds considerable stress to the marriage; divorce too often follows. Of the ways I have listed here, this is the hardest path for a JW and non-JW couple to follow.
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(Words and phrases in bold italics have specific meanings to Witnesses. Learn their vocabulary, so you can understand what they are saying.)
[edited to fix paragraph beaks and to highlight reinstatement]