I try to keep it organic (meeting in game), but my very latest couple is different.
Bailey was a single, young adventurer splitting her time between Sulani and Selvadorada. Upon aging up, I decided it was time to try dating at least. Because I felt like playing aliens, I put down a single alien Sim from a previous project. Enter Darin. It happened to be Monsoon season on the islands, so I had Bailey go and rescue Darin and offer him shelter. It took a surprising short time to be able to “Ask to join household”. He was on a camp bed in her main room, but eventually one thing led to another...
I have also just introduced a third character. Another alien named Kailee, who was supposed to be Darin’s spouse in an arranged marriage. Which Darin ran away from. Darin and Kailee are childhood friends, but he doesn’t want his elders organising his love life for him. I put Kailee in game, cheated an appropriate relationship level. She turned up in a bar during an offical date! Now Bailey is mad at Darin (but will probably forgive him, eventually).