I made a mistake on my I-129F, got an RFE, responded to the RFE with what they needed within 10 days and got approved just 4 days after they received my response. If they RFE you for the letters of intent, it's a pretty easy fix
I can't agree with this enough... when you find your person, it sucks to be separated but once you get past the separation part of the immigration process and are together here in the US, all the hard times being apart fall into the background and you realize that it was soooo 100% worth it