I knew a couple who went to Retrouvaille and they are still together (it's been a few years) and although I haven't seen them for a while, last I did they were happy. They had been talking "separation" prior to that.
Before my non-ex and I divorced, my very traditional Catholic priest really tried to get us to go. It just never worked out where we could attend a weekend, and, we did eventually divorce.
Unfortunately, when mental illness is the cause of a problem in a marriage, the mental illness needs to be directly handled by an expert in the field of the mental illness. Retrouvaille is just not that. You can handle the symptoms one by one with various communication techniques, and maybe you'll learn a technique or two from them you haven't here and in therapy, reading, research, etc., but ultimately Retrouvaille isn't set up for mental illness.Edit:
DBT is usually the best thing for BPD - so I'd call and ask, or email Retrouvaille and ask if they know much about PD couples, or can recommend a trained person to help you in your area.
This is very good advice! Retrouvaille is a Catholic ministry, and they may well have someone they can refer to you who is both a therapist and within the scope of the Catholic faith (incorporates religion into the therapy)