I am(/was?) a single mama and never found it a problem to date guys or have boyfriends. Well, not to get dates... actually figuring out where to find a babysitter or find a family friendly way to spend time together was a little more difficult!!
But yeah, as lots of other people have said, it sorts out people that aren't worth your time. Not to say that it's easy though!
I've now found a rad guy who I've been with for two years and who I'd like to stick with. He's the first guy that I've let take on some of the parenting responsibility. The other 2 (serious) boyfriends I've had, I wasn't prepared to let them have that sort of relationship with my daughter. I was still a single parent, even though I had a partner. Now I consider myself a co-parent.
Anyway, it's an ongoing learning curve. This co-parent business is a lot different to the freedom of single parenting!!