I know but my theory is that Gabby has been a victim of domestic violence for quite some time but due to her dependency on the guy, kept quiet about it.
I also suspect that after all those weeks on the road with him him, she probably couldn't stand it any more and wanted to go home and that likely set him off.....
Recall the 911 call from passersby that reported she was getting slapped around by the guy but when the officers showed up, she made no mention of it at all. And in fact allowed the boyfriend to claim she had hit and scratched him.
I think she was terrified of what he would do to her if she had told the truth.........That happens all to often when long term victims of DV fail to tell the truth to responding LEO's and refuse to press charges.
However, her friends that knew them both from HS tried to discourage the relationship. That speaks to him having issues since HS.
Toxic relationships often end up battering each other physically. Never ends well either. This one sounds like it fits that bill.