The girl I’m in a relationship is my FP, and I’m hers. 
The positives are that we both love each other intensely and deeply, which satisfies both of our needs for affection and attention. We both want to be around each other constantly. We both understand BPD and FP struggles and know how to comfort each other when needed. Also we’ve never argued but are able to take breaks when we need them.
Not many negatives except worrying one of us loves the other less or more, and typical BPD struggles that happen in our relationships with anybody else. On my side, I’ve struggled with the dreaded pedestal- at the exact second she expresses any indication of needing time alone, I question whether we should be in a relationship- but I’ve since recognized this as a symptom of BPD and can handle it. Also extreme jealousy, but can handle this as well.
What’s your experience, even if you’re not your FP’s FP, or your FP doesn’t have borderline?