I'm following that case very closely. The thing is, a creepy "ghost creeper" was described by two other women months before the couple was killed. Further, they had given a description of this person (who had established a dry camp near where they were dry camping on what may have been BLM land - although locals say the area may be privately owned, no one seems sure and LE hasn't said). One of the women told a coworker that if they ended up murdered, it would be the "creepy guy" and they were thinking about moving camp (where they had been living for a while). These two women are part of a large group of young people who camp outside Moab, either in established BLM campgrounds or in dispersed camping (the murdered women were in an unusual area, in dispersed camping - an area that locals say they know, but which is not part of the BLM camping system - no water, etc).
The two murdered women went into town the night they were killed and once again mentioned that this man (who had been camping near them, also for a while) was "creeping" around and scaring them (I wish people would be more specific!)
So I don't see how it could be GP's BF. The fact that the murdered women had told more than one person of their fear of this man - over a period of time much longer than the time GP was in Moab (one night, as I understand it), means it can't be GP's BF.