A good article (in the TIPS section recommended by Cat Familiar) is:
What Does it Take to Be in a Relationship with a person with BPD?
This section stood out to me, as related to your question:
Preserve Your Emotional Health: The intensity of emotional reactions, and the rage take a toll on even the strongest. Since you cannot escape the natural human impulses to "recoil when raged" upon or "be overly protective" when idealized, it really important to have other outlets / escapes to keep yourself grounded. It's important not to become isolated. It's important to have a significant emotional support system for yourself (e.g., close friends) that goes beyond the relationship.
Let us know your thoughts;
kells76