I have never had marriage/couples counseling. However, what I would expect from it is that the T supports both parties equally. Or supports neither. He shouldn't choose sides. Relationship problems are never a one way street. It's always both people (almost always, of course there's terrible abusers, but I don't think that's the question here). And in that case, the T shouldn't just help one person get their way, he should help both to find a compromise.

For things such as helping your wife with suicidal thoughts, with your boundaries, with other peoples boundaries, with her emotions and so on, she needs to go to individual sessions. There, the T will more or less take her side, where it is appropriate, and help her stand up for herself.

I think that what you are getting there is not marriage counseling, to me it sounds like the therapist is enabling her. I don't know whether she actually has BPD, but as somebody who does, a therapist that would say that it's okay to do everything she wants in a relationship would be one of the worst thing that could happen to me. Mostly because accepting boundaries is very hard with this diagnosis, but at the same time it's very necessary.

Finally, I'm a bit bothered how you say he "convinced her to stop talking about suicide". I'm not quite sure what that means. I can, of course, understand that it would be very bothersome if your spouse goes on about wanting to die every day. But since you only see this therapist together, that means she just doesn't talk about it, right? Which doesn't at all mean she is not thinking about it. I don't think that's the way to go, I really think she should have a individual therapist, plus if you feel the need, you two together should have a marriage counselor that you both feel comfortable with.