If you don't lay down some barbed wire and heavy duty moat between you two, she'll think she can cross that line at her leisure.
Put up some walls. Don't talk to her or your mutual friends about how you feel about her. If you have to talk about it, find a family member or unrelated friend.
Don't let her in on your business. Avoid her whenever possible. Never be forthcoming.
And if she asks you personal questions, don't answer them.
A man is a man is a man.
You're John Wayne, she's just a dame.