Dearest Emi,
There have been lots of questions suggested. Some of them could be tough, and your SO may have trouble answering some.
What I think is possibly more important than what you ask is HOW you ask. It is far too easy to approach a question with bias and preconceived expectation. This can shut down an honest and fully open response. Questions that come across as accusatory or loaded can put people on the defensive. Little subtle things like saying "Don't you think..." Implies that they don't think or if they disagree they are wrong, and establish the questioner's stance even before the answer is given.
It's hard, but try to frame your questions in a more positive tone. Don't ask "You aren't going to transition, are you?". Rather you might ask "If you had the opportunity to transition, what would that look like"
Good luck. You seem like a strong and loving person and you SO is blessed to be with you.
