Cisgender woman here, I just wanted to add that if my husband were to come out as trans, that would not be a tragedy or something I wished he’d gotten figured out sooner for my sake. In this hypothetical scenario, if it somehow managed to make us incompatible as married partners we’d deal with it but people have gotten divorced for much worse reasons before. The worst part for me would be worrying if he’d been miserable during our marriage, because I love him and would hate for that to be his experience of our time together.
It’s really hard to imagine because AFAIK we’re both cis but personally I’d probably prefer to stay married to my spouse even if he changed his gender identity. I mean he’s still the same person I married and we still love the same things and have a wonderful life and child together. I dunno, maybe it wouldn’t work out in the end but I sure as hell wouldn’t be mad at him for something he couldn’t change.
Anyways, my point is you don’t have to assume that your relationships with cis people will all get blown up if you do happen to be trans. I appreciate the urge to have your ducks all in a row before embarking on significant life events but the truth is that marriage and adulthood is super messy anyways. If you marry someone and have a kid with them the odds are good you will have all sorts of chaotic events to deal with- physical illnesses, mental illnesses, kid stress or illness, weight gain or loss, money trouble, job changes, changes in personality with age, the list goes on and on. The trick to being happily married is rolling with the changes, working hard at your partnership, and being committed to your partner, not having it all perfectly lined up at the start.