Single sims don't stay single very long in my game, outside of a challenge is the only time I have single sims until the challenge tells me so.

My single Sims all have a reason for being that way. I play their stories accordingly. So anything could happen to those Sims, depending on their motives and what happens elsewhere. They might marry, get a partner, move into a special household such as the monastery or prison, move in with friends, go to university or stay alone, according to what makes sense at any given time.

I never play roommates, one of my mods mangles the code and I've never figured out which one so I just avoid them.

I have a lot of bigger households so single sims can be quite a nice change, to only have to focus on one.

My single Sims just do the same things over and over and over and over and over and over until I finally scream and move in someone else...or get a pet.

Actually no, my biggest single Sim is Amy Single. She is romance and has a very happy and fulfilled life with just her and her cat. Sometimes I will allow her to have a baby, whether an oops or an alien pregnancy. With Risky Woohoo installed an oops is more likely

I've had neighborhoods full of them. What I've done in the past is to create roomies for them by using the hacked "Tombstone of L&D" which will generate single men or women for the purpose. I've given them opposite sex roomies, or same sex roomies. It makes for some interesting happenings because the roomies will have graduated from college and have a few skills, where the newbies do not.

I love watching relationships develop from such things.

I used to make families in CAS to start off with but it just gets too annoying. Whenever I create a single sim they start in college so I get my sim prepared for their career but I try to keep them single for a while so I don't have to deal with taking care of other sims but I end up getting worried and take too long and I have to have my sim marry. I usually start them out in a starter home and deck it out with the money my sim earns in different ways. I love giving my sims pets but it is also annoying to deal with for me, and I got my sim a roommate.