how come there is this one awkward question meh? don't want to talk about it. but, anyway. here's my view.
single : can do whatever you like. no restriction(except from family). doesn't need to think about others. you can flirt all the way without feeling guilty.
double : you have someone to think about. you have someone to turn to. gave you support even when it is the last thing you needed. you have someone you can be silly with.
there's more. endless list. for both la of course. i like a quote from hanis zalikha. she said, "have you ever wondered if maybe you don't really miss the person, you just miss the routine." hmmm. could be. who knows what we really feel, right?