Folks,
We don't know what was going on between Jonathan and Erin. Some men internalize the trauma of miscarriages and blame themselves for "hurting" their gf/wife. If Jonathan shut down emotionally, Erin could have, alone in a strange "city" turned to a friend for comfort. Jonathan may have even known this and they may have been working it out. It happens. While this rumor (sorry, but that article has wicked sketchy sources, so I'm still calling it a rumor) is disheartening, it in no way makes Erin or Jonathan any less victims at the moment.
An affair, while to a generation before may have been a deal breaker, in some couples today, it can and is worked through or not a big deal.
We don't know what their marriage arraignments were.
As for eloping and a somewhat spontaneous wedding, my guess it was to get on the housing list. I had a friend who eloped in college, 6 months before she was supposed to get married, to get on a base housing list. She literally got married and came back to the dorm and her roommates for the rest of the semester. She had another wedding later. Military people do that. It's just how you have to work the system.
As for the confusion about 2 months or 3 months pregnant, she's 19 and miscarried 6 months ago. Her body might not run like a swiss clock. Between that and the doctor saying you're pregnant from your last period and not from date of conception thing, tons of people get confused.
I think Jonathan is innocent and I don't see Erin being some evil seductress. I think they were young sweet kids in love in a really complicated and ever changing situation. Sometimes people make less than stellar decisions. No one deserves to go through this though.