How do you get you sim to get married (or budding romance or something)?

I've had that problem before too. What i did is kept insulting them until you are in the disliked area. then keep being romantic until it does something. if that doesn't work, go to the menu on the bottom right and where it shows your "disliked" status, underneath it, it should say "budding romance." Get that up until it's official and then it should show that instead of your "disliked" status.

If the explanation above doesn't work, try being romantic with someone else.

You cant be in the best friend zone to marry. you have to be be in the freind zone, and then start being romantic with the person your trying to marry.