Delirium,I honestly think it's possible that your friend has your best intentions at heart. However, I know it's frustrating and annoying when people close to us think they know what's best for us and refuse to accept our own ideas. If anything though, it sounds like she's wanting to strengthen your relationship with your boyfriend, as "she" believes you two getting married will do that. And, perhaps she thinks you'll regret not having kids down the road, and doesn't want you to have those regrets. Of course, "you" know your relationship is strong and that children aren't for you, but nonetheless, she is obviously having a hard time identifying with your views. I don't think this means she doesn't care about you.
Close friends are hard to come by, and if this is the only problem you have with her, it's certainly not worth dumping the friendship over. I would explain to her that while you know she's only looking out for you, it upsets you nonetheless, and you'd like it if she'd just accepted your feelings towards marriage and kids, and left it alone.
As for social stuff in general, yes, I think there will be challenges down the road, however, so long as you know that you know you are doing what's best for you, it doesn't matter what anyone else thinks. Feel "thankful" that you have the presence of mind and foresight to live "your" best life.... as, sadly, not everyone is so lucky... so many just follow everyone else. Secretly, there will be a lot of folks wishing they too had a child-free life like you... all you can do is feel compassion for those people.
Good luck!
Back to topic..............Not having to be worried/stressed every second of the day over matters concerning your children!!
Not having to be a "counselor" for the "rest of your life" to your kids!