It is far beyond a faux pas. This is much more than a mis-step, much more than a break with social norms. This is down to a level where we as a society SHOULD judge. Ron might very well need comfort. I do not begrudge him comfort. I DO have reservations, and quite strong ones, that he would seek his comfort from a child. Misty is a child, no matter how street-wise she may appear. If he is not thinking with a clear head, then it should be the judgment of society to say "Dude, marrying a teenager while your daughter is missing and presumed in extreme danger at the very least and most likely dead is a bad idea." I simply don't believe that society saying that to Ron will make it heard. It will just be one more opportunity for him to believe it is him against the world.
If it is the second thing, "the felony he's looking at" (I assume you're speaking of him perhaps facing statutory rape charges) then should he be allowed to tie this young girl to him legally, when legally the world views her as a victim of a sexual predator? That's what statutory rape is. The child is taken advantage of.
In either case, her parents are obviously signing the paper. It makes one wonders how many times they've handed her over to be victimized.