Straight 20-something here, with no children and no plans to be anything other than a great aunt.
As to the children in bathrooms issue, I will say that while I have been taken aback by seeing older children who (from outward appearance, at least) identify with the opposite gender of the bathroom they are using, it takes but a moment to remember that (a) these children are, or should be, their parent or guardian's treasure, and safety is a priority over all else and (b) there may be circumstances not immediately apparent that make the "right" bathroom the one they're in. The most outrageous bathroom behavior I can reasonably imagine occuring - children peeking under stalls or exposing themselves in the public areas of the bathroom - may be a consequence of the special circumstances relating to the child that the parent/guardian does their best to rein in, but of course, none of us can perfectly control the actions of another person, even - or perhaps especially - when those other individuals are children. A prior poster noted the special bathroom-related challenges faced by children with Aspergers. Any number of other special situations may exist. I aspire to keep in mind that normal is a relative standard and pause before I pass judgment.
Now on to the OP: I want to chime in to encourage you and your partner to embrace the "Disney magic" and enjoy being yourselves. While Disney is wonderful in and of itself, I find that what I treasure most is not the magical moments themselves, but getting to share them with the people I love. Your fabulous partner is the person you fell in love with, so I hope you'll be able to share the Disney magic with him, and not some watered-down version of the great guy I'm sure he is.
Have a wonderful time, make some great memories, and of course, report back after your trip!