I can relate as well. The only thing that saves me from isolation is my extended family in the area and my co-workers. Other than that, I never find the time to visit with friends, especially the married ones. Of course, coming the Mothering boards and finding like-minded mothers like yourselves is a great for helping me feel like I'm staying 'connected'.
As far as dating, I haven't met a man that I consider worth giving up free time with my daughter for (she's 20 months old). In addition, I've made a promise to myself and the emotional health of my daughter NOT to introduce her to a parade of men that she becomes attached to and then never sees again. Not only do I not want to put her through that, I don't want her growing up with that as an example of how to conduct adult relationships.
I feel really strongly about this as I've worked with kids of parents who have a constant parade of 'SO's' going through their life and the emotional damage it wreaks on the child is SIGNIFICANT. Not to mention how it effects their future choices and patterns regarding relationships.
I've also personally known too many people who choose a relationship over their children's best interest.
That's not to say it's not possible to balance both in a healthy and positive manner, just that I believe before introducing a mate into the picture and a child's life the parent needs to be pretty darn sure this person is likely to be around for a LONG time, as well as be a positive addition to the child's life.
Just my .02!