When you argue with hardcore Christians who are uptight like that, 99.9% of the time you won't win. It's best to just not say anything to them, because they won't give up. I am with you though, I 100% agreed with you on when you said
"Well, some of us don't plan on getting married, or having kids. Namely me. And if God really DID love us, then he would want us to be happy, and that means having feelings for whoever we please."

That is true. Although I believe in God 100%, and I try to do whats right and everything, I also believe that people should be happy, and if one doesn't want to get married etc... thats their business, and nobody else on this earth should come between them and their decisions bc it's quite frankly, none of their business. Your friend is a hardcore christian it sounds like, and from reading that, it sounds like she was trying to shove her beliefs down your throat. I don't like people like that, sorry.

To each their own I say.