If you just found out, you're probably not reading this calmly, and that's completely understandable. You don't need a plan for the rest of your life today. You need to get through the next two days.
Try not to make big, permanent decisions right now
Whatever you're feeling right now, whether it's rage, numbness, or something in between, is a normal response to a real shock. It is usually not the right moment to file paperwork, confront anyone publicly, post anything online, or make a final decision about the relationship. Those decisions will still be there in a week, and you'll make them with a clearer head.
Tell one or two people you trust
This is not something to carry entirely alone. A close friend, a sibling, or a therapist you can get in touch with quickly can help you just by being present. You don't owe anyone the full story yet, including people who ask.
If finances or safety are a concern, take a few quiet, practical steps
You don't need to act today, but it's reasonable to make copies of key financial and identity documents, note your account balances, and know where important paperwork lives. If you feel unsafe in any way, that changes the priority entirely: your safety comes first, and the National Domestic Violence Hotline (1-800-799-7233) is available right now, 24/7.
Take care of your body
Shock affects sleep and appetite more than people expect. Try to eat something, drink water, and rest even if you can't sleep well. This sounds small. It isn't.
When you're ready, and not before
Once the initial shock softens a little, usually over days rather than hours, it can help to talk to a therapist who works with betrayal trauma specifically, and if you think divorce or separation may be part of your future, an early, low-commitment consultation with a family law attorney can just help you understand your options, with no obligation to act on anything yet.
This is general guidance, not a substitute for professional support. If you're in crisis, call or text 988 any time.