How can I be a strong man that makes his woman not cross the line?

Knowing the nature of women after redpill, I feel if I say something like “if you do this then I’m walking away” will make her go out of her way and do it just to test me. Any suggestions for a girl to respect a boundary I set and overall be more submissive? For example if I say “if you sleep with him again then I’m not talking to you anymore” or is that too much and should it be more subtle?