For me, the calculus is simple. I’m twice married, once divorced, and still with #2 after 23 years. We had (have) separate careers, names, bank accounts, and home offices, but we also had differential estates (I owned property; she didn’t), I had a child; she didn’t, and there were various other individualities. It made no sense to marry, unless we had issue (children). Then, the equation turned upside down. A man has the most rights with respect to his children when he’s married to their mother. As soon as she got pregnant, we married.