I can speak from experience here, because this actually happened to me!

My partner (born female) and I married in our late 20s. He was already casually gender non-confirming before we married, and I described myself as hetero-flexible. His transition was rather gradual, with no strict coming-out event, but it was something we discussed openly. After he began presenting as male on work settings, I began identifying myself as bisexual.

It worked out very well. As the person above noted, you can really call yourself whatever. If you wanted to, you could identify as straight with an exception made for a single person. Although I would advise against it, as your partner might take some offense, and it confuses people if you identify in a way that conflicts with your long term partnership. Most co-workers assume I'm gay because I'm married to a man, and I don't bother to correct them.

Sometimes it comes up, because my husband and I have a biological son together, which isn't a secret. Sometimes when taking about him and genetics, it leads me to explaining all of this. But as you can see, it's unusual, but not that hard to explain.