Depending on the traits of the Sim, you can get wishes to have the first kiss, go steady, propose marriage, and probably some others. I think a Sim who is a Hopeless Romantic will get some special wishes along those lines. Also, as the relationship progresses, those wishes will come up for a particular Sim. This is often how I know my Sim likes someone in a romantic way... she'll get a wish to kiss him. Another wish I've seen is to get married. Not to anyone in particular, just get married. It comes up sometimes when a Sim is a pregnant celebrity.