Why can't my ex-wife take a hint here?

From one nobody to another, the only thing I can say is that neither you or your ex wife are obviously mature enough to have a kid, but she is here and needs both her mom and dad to grow up. You are divorced, but I think that you don't want anything to do with either your wife or daughter, and well, that is your choice. Your ex is just stressed out, that's all, come on, have a heart. She needs a little more help and is overwhelmed. You can always ask a family member to help, or at least get a good babysitter and show a bit more compion. You have a little girl that probably does not fully understand what she did wrong to make her father reject her like this (Kids usually blame themselves when their parents act like you do). Just think, she is your child. Your blood. Your family. What her mother does is not her fault.