Okay, River, thanks for educating. I think you have a healthy approach to this--even though your thoughts about sex seem to want to dwell on romantic love only, you don't expect the same of your partner.
I think that's good, because nobody can or should expect to control their partner's thoughts. If Mrs. Cheesehead really is asking that Mr. Cheesehead keep all his "thinking about sex to the context of loving relationships, with her and with others," (we'll have to ask her if that's what she meant) then she is asking something impossible. Mr. Cheesehead can't keep all his thinking about anything to the context of anything. We can't control what we think about, and if we try, we're just pathologizing perfectly normal brain processes.
We can have boundaries about what kind of actions we will tolerate from our partners in relationships, but it is not reasonable to have boundaries about their thoughts.