You should have showed her in actions that it was more than a sexual thing. Words are just words if there are no actions to back them up. Sex and not much else is not an actions word that indicates that you love one another. Giving her money is not an action word that shows her you loved her if all you're seeing her for is sex. You didn't offer her any part of your life or, if you did she didn't want it. If it was any other way then what I just discribed then you two would be husband and wife and that child would be yours.
If you look at it more pragmatically, more logically then perhaps you can just forget about her a little more easily and stop contact with her altogether. Did you expect a part time sexual experience to last forever? That she'd be satisfied with once a year sexcapades? No security?
Yes, the least she could have done was tell you that she wouldn't be contacting you anymore, that she has someone else now thats she's carrying another man's baby but heh, that would take closing a door. Codependents rarely have the strenghth to outright exorcise their codependent partners completely out of their lives. They always need a safety net.
Whether or not she said you'd not keep secrets is neither here nor there. As I said, words are just words. It's her actions (or in this case lack thereof that tell you her truth.)