Go into CAS and create the Sim you wish your Sim to date. Put them into the neighborhood and have each of them get on Simstagram or one of the other social medias available. Find a way for them to 'bump' into each other. No, it's not easy. It's never easy until you've restarted the very same save so many times that when the two finally bump into each other at a venue, they fall hopelessly in love on sight. LOL (Yeah, that's how it's happened for the latest three iterations of my same Sims.) Best of luck and hang in there.