You shouldn't marry someone unless you truly want to be with that person, personally, specifically, for the rest of your life.
This was inconceivable to me when I got married. I was young. I couldn't see further ahead than next week.
And the priest was very dubious about marrying us. He kept asking 'Do you believe in divorce?' and I kept responding, 'Well, it's a literal fact. How can I not believe in it? I'm sure nobody wants it when they get married.'
But at the back of my mind, there was always the thought that, 'Hey, if I meet somebody else that blows me away, or I really start to get bored, what's stopping me?'
For me, that stuff changed as I got older. I think there were really two major things that changed how I stopped seeing marriage as contingent and temporary, and started to see it as something permanent that you put before everything else.
The first thing was having kids. Sure, step parents can love your children -- but it's inconceivable to me that they'll love them as much as I do. And there's a not-insignificant chance that they'll be assholes towards them. I know this because if I put myself in that situation, I'm going to favour my own offspring over the kid from another father who came along with the mom. I'll try really hard not to let it show, but if they're both drowning and I can only rescue one....
The other thing is loyalty. I'm an asshole. I've got my positive qualities, but like most men, I'm a fucking baby. Selfish, self centred, inconsiderate, all the flaws that we associate with men. If somebody is prepared to put up with me -- more than that, if they're prepared to love me, despite my flaws -- the very least I can do is to return that loyalty.
I wish I'd figured that out sooner than I did, but better late than never.