Thank you all for your replies.

Based on what you've said and my other readings on the subject today, I believe that BPD could very easily be the issue. She actually had a really terrible outburst last night that resulted in the both of us recognizing that something needs to change or this isn't going to work. I think she might actually be receptive to the idea of going to a psychiatrist and seeking treatment for it. I'll bring it up to her soon, and hopefully she won't take it too badly.