You can try to explain it away all you want but if it looks like ANYTHING at ALL like a wedding ceremony, registered or not, you can very well be denied. We have seen it happen many, many times in the past. Too many times to count. It is not a risk I would be willing to take.
Just get married and file an I-130 for a spousal visa. It's far less expensive, spouse gets green card when entering the U.S, so no waiting to work or leave the country and the processing times are virtually the same.