I think one of the main attractions to having a significant other must be to have someone to DO stuff with. I know it is for me. The ironic thing is that as a relatively active person, I have spent a majority of my life without such a convenient resource. I have been active in spite of it, I suppose.
Seeing others (especially a former S.O.) doing fun stuff with their S.O. can be frustrating, and I have felt my share of jealousy, but I have to admit, I have been *very* fortunate to find a variety of people to fill my need for a companion. This coming weekend, for example, I'm going to Las Vegas (for the first time) with my sister, my friend Stacey, and a couple other gals. It's going to be a heck of a lot of fun. My trip to India will be with yet another pair of friends.
I'll probably never rid myself of the impression that a S.O. should also be a co-conspiritor, but I'll give myself the credit of not falling prey to the inverse, that a co-conspiritor must be a S.O.