Yes. She has been dealing with mental illness for some time. The most recent diagnosis is BPD though i take little stock in diagnosis. She does manifest many of the characteristics associated with the diagnosis. I stumbled across the board and saw that many threads dealt with the emotional bulldozer she can be and how it effects a significant other.
OK, BPD traits are extremely stressful for a significant other (SO). It can be so complex and confusing.
You're right diagnosis in itself, is not a cure-all, in fact it is just a start. Did she get herself diagnosed?
In terms of yourself, there are many helps on this forum. See the Lessons on the RHS of this page. There is a lot of good info in there as some tools and skills to learn, experiment and apply. It takes time to understand this stuff, but it's well worth it.