I'm not sure that I'd side with the girl (Jesse) in this part. It didn't say WHICH ONE decided it wasn't going to work. If the condition of her house was any indication of how she lived day-to-day, I'm not surprised things didn't work out. The guy (Brian) hadn't been out of the Marines for that long - while it's not true for everyone, there is a reason they say "once a Marine, always a Marine". Her clutter and chaos would definitely go against the cleanliness and order the Corp taught him. While being a messy housekeeper isn't necessarily the sign of a mental illness, I'm not really sure there weren't some "issues" for her as well. She was the one ready to go off - with her parents blessing - to a TRUCK STOP to meet up with a guy she'd "known" for about a year.
The "weapons of mass destruction" thing was blown way out of proportion (pun not intended). While having PTSD can put a twist in your shorts, it doesn't necessarily make you unlovable, doomed to living life alone because you MIGHT get angry.