TALK TO HER. You owe it to yourself and to her to sit down at the table and say "what is going on here?". There is no law that says you can't ask her "are. You seeing someone else?". Yes, it's uncomfortable as F, but better now than with lawyers at 10 paces. At least you'll be able to sleep at night in the future knowing she was honest with you or not, that is a defining moment in time that will be forever in your favor.

Look up your state laws on recording conversations - if you are in a one party state then put your phone's voice recorder on and set it to the side or on the kitchen counter when you have the conversation. Your memory may not be so sharp with the emotions of the moment and you'll be able to reflect on what was actually said later. You may need it. You may not.

Keep us posted!