Sounds like you're in the right spot to me so far, but I think I am right in adding that it takes a professional's opinion to know "for sure". BPD's share SOME traits with other disorders... .pretty sure that's how it got the name "borderline", because it borders so many other disorders. So, if he is willing, it would probably help you a great deal to get that professional opinion... .but I also know you can't "push" a borderline to seek help. They really must reach that conclusion on their own.
Having said that... .
I've gone through the "lessons" on this site, and I think they could help you a great deal in determining whether or not you're "in the right spot". As you go through them, you might quickly spot things you're very familiar with. It does sound like he idealized you in the beginning (put you "on a pedestal"?), and then began devaluing you once he felt comfortable that you weren't going anywhere. And that does sound very BPD.
My partner only ever yells at me. With everyone else, she is extremely patient and forgiving. Someone could straight up call her the "B" word, and she'd just smile at them and say "sorry you feel that way." But I can say something not even remotely hurtful, and she can turn it around and make me sound like the most evil person you've ever met.
And let me blow your mind right now: I've started taking it as a compliment. Why? Because I understand BPD a lot more now, so I know she only explodes on me because she trusts me. She trusts me not to abandon her or resent her. She feels SAFE with me. She doesn't feel safe with anyone else, and that's why they are all safe from her outbursts. Ironic, hey?
I'm not saying YOU should start taking it as a compliment. But maybe it will give you some insight into a BPD brain.
Good luck to you and best wishes
