I feel like it could benefit us both after the long and damaging relationship we've been in over the past four years.
Can you speak more to that "feeling" you have?
I'd also suggest that you speak to how it would benefit you and how it would benefit your gf as separate sentences. Especially if you talk about open relationships, because the benefits (and challenges) of them are not the same for both people. Not even close.
I'm also curious--is there a specific person that either you or she (or both) are interested in right now?
Does anyone have experience or knowledge of how BP's handle being in an open relationship compared to the general population?
Most of what I read about open relationships and the experiences I've had are that when you add more people, the need for skillful and clear communications goes up significantly. Many pwBPD cannot handle intimate communications or conflicts well in a r/s with one person... . that only looks worse when you add people!