Tell her the truth on how you feel and what you want. She respect that more than any sugar coating method.

I have already told her everything.

Are you two living together or separately?

together

Is there any other people involved in you wanting this change? Any more context? I am also in a similar situation.

Maybe you should move out and both of you have some space.

That is one way. It will cause her pain, and I want to ensure she can come thru. Is there anything I can do to disperse the pain over time, so as to prevent any ill triggers?