You remind me of my cousin and her ex-husband. We have a stodgy Old Maid aunt who used to go on and on about couples living together. I don't think she was ever aware that my cousin lived with her (now ex-)husband for several years before they married. I think she thought I would be the one to do such. Anywho, I guess those years of deciding whether they were compatible for life did not pan out because he found a younger version after 15 or so years of marriage. I think he might want children or some such at this point in life rather than the freedom he cherished at 20. So, my cousin is childless and husbandless at 39. And brokenhearted. But at least they had a try-out to make sure they would be compatible.
Life has no guarantees any old way you slice it. People change. Sometimes for the better. Sometimes not.