only flirt/romance relationship can marry (after propose event) from the 3 options when you 1st chat with any sims.
2sim = 1 story
if its an oppsy wrong i need delete
= either restart game fresh if you dont mind lose everything you have now
= cash and open 3rd slot (just need +1 since 3sim = 3story)
= just play that sim till they retire ( just keep play get traits jobs hobbies, option will be there later on. days after)
i recommend just play since getting a story complete will give you special outfits for your wardrobe
and a retired sim will drop you heirloom
likey me if you feel this = helpful thx