Sorry to hear about that.
You would first need to get married and send off AOS paperwork, I would include AP expedite request in there too. A recent note would be helpful.
However, keep in mind that USCIS’s understanding of an expedite is different, it can still take several months to process. Also, it is not guaranteed it will be approved.
If it is pertinent to return urgently, then I would get married, leave the US and have the USC spouse file a petition for the spousal visa process, this would take 18-24 months