I'm not an expert here but here is how I understood it:
If she decides to marry her BF, then that would fall under F2A Preference I think. She must file for this type of petition. If how long would depend on what the current priority dates are right now, last time I checked it was for Jan 2010.
Not sure if they would allow him to visit the US since he is already married to the petitioner. Maybe, they could postpone the wedding first, let him apply for a US tourist visa, if approved, he can visit her, then they could get married in the US na lang. Then, if that happens, he could probably stay na lang sa US and wait for his documents to be processed. This is just hypothetical ha. Not sure if this can be done. But I really am sure that if they get married, I doubt that he can just visit her here.
The consul would probably say that they are already married, thus he has to wait for his petition to come through before he can go to the US.
Just my two cents.
It would probably be best to ask someone like Harley Barrales for a more concrete information.
Hope this helps.
