Help Needed!

I feel my partner and I have drifted apart and I'm wondering if there is anything more to it than that on her part. I have already drafted a list of things I want to ask but I want to do it in a way that I can get the honest answers.
I am going to pre warn her and ask if she is ready to talk and whatever her answers are I will still treat her the same and do the things for her that I had promised (such as her tax return which she doesn't like doing) in the hope that this allows her to be honest.
The things I'm asking so far are:
How does she see our relationship
Has she been with or dated anybody else (the obvious one)

Does anybody have any ideas of what else to include or how to ask a specific question?
I don't want to upset her as she is a good person even if it does turn out she has been doing things I don't like.