I'm in the opposite as you. I have a three year old son, and my g.f doesn't have any. It definetly shows how much she cares for me.
The thing you need to realize is like what Austin said. I have shared parenting (for now Atleast until court in may, then I should have full custody). When I'm off work I have my son, except for a couple times like Wednesday night and every other Friday and Saturday. So chances are actual going out on dates will be challenging. Unless she has a strong family network that will babysit at the drop of a hat. My family isn't close in distance, and the ones that are it's pointless to ask them. So basically dating will most likely be taking the girl out with her daughter. So think family every time.
I have the crazy ex to deal with and it does complicate things. Because if she does something stupid with my son (i.e. parenting completely wrong, shit with her bf, pick up/drop off complications) Then a lot of the time it puts me in a shitty or short mood. This will affect your relationship if she's not understanding. My gf is amazing with my son and her family is as well. I think if things weren't this great we wouldn't be together still. And it's nothing wrong with her it's just I'm 24 with a failed previous relationship and don't want another long term one. But the relationship between her and her family is worth risking another long term relationship over my previous insecurities.
When I met my gf she told me she never wanted a kid, just as your stating. Which was perfect for me. My son has a sister so he's not an only child. So since he has a sibling to play with, so I'm done with having kids. We've been dating for a year and the longer and longer the better and better things are between all of us. Now here's the complication. Things have gotten so well she's changed her mind from not wanting to have kids to wanting to have one with me. I still haven't changed so we've had a few fights over this.
Basically there are good things and bad things as to dating someone with a kid. If you do date you need to sit down with her and go over everything. Be realistic and able to compromise. Also don't get so comfortable with spending a lot of time with her and her kid. Make the effort to get a baby sitter and take her out. She's not just a mother she will need this too.
If I were to break up with my gf it would make my son pretty sad. And it his is something I don't want to do, but something that could happen. If I were to ever break up with my gf I don't think I would date someone with a kid. There are too many variables to change shit.
Also don't fall for a gold digging whore. A lot of girls just want someone to be the father of their kid. You end up getting so attached with the kid they treat you like shit. This is happening to someone I know now.
Good luck.
