What are your thoughts?
Do you think it's best to live with someone before getting married?
Aside from religious reasons, can you see any reason to NOT live with someone before marriage?
Yes. Lots of them.
It makes it entirely too easy to simply "drift" into marriage, rather than making a definite, affirmative decision that THIS is the right person to spend the rest of your life with. I cannot count the number of friends I've personally seen start dating someone, move in together after a couple of months because "it's what you do", and then just kinda succumb to inertia. It's not fantastic, but it's not horrific, so they just go along, not especially happy but not really thinking about it, and the expectation and pressure to get married subtly builds up, and one day they do it, probably for boring, prosaic reasons. And almost inevitably, the marriage collapses within five years because they never really, affirmatively wanted to get married in the first place. It just happened by default.
Hand in hand with that, cohabitation makes it a lot harder to extricate yourself from a lukewarm, less-than-marriage-quality relationship, and commits you far more than the relationship might warrant before you're ready to REALLY commit.
In a weird way, I think it also has the psychological effect of subtly conveying to both your partner and yourself that the relationship isn't really important to you. I realize that's the exact opposite of what's intended, and maybe even what you consciously believe happened. But dramatic scenes in TV and movies notwithstanding, there's an excellent chance that the decision to cohabitate probably was not a huge, romantic scene almost identical to a marriage proposal (see above re: "drifting into commitment"). Even if it was, by making a halfway commitment instead of essentially pissing or getting off the pot, you have on some level signaled yourself and your partner that you view the relationship not as "'til death do us part", but as "as long as I am happy and comfy".
To some extent, this is just my perception, but it's borne out by statistics. A Columbia University study found that only 26% of women surveyed and 19% of the men married the person with whom they were cohabiting. A National Survey of Families and Households, based on interviews with 13,000 people, concluded, "About 40% of cohabiting unions in the U.S. break up without the couple getting married." The National Survey of Families and Households also indicates that "unions begun by cohabitation are almost twice as likely to dissolve within 10 years compared to all first marriages: 57% to 30%." Psychology Today reported the findings of Yale University sociologist Neil Bennett that cohabiting women were 80% more likely to separate or divorce than were women who had not lived with their spouses before marriage. Etc, etc.