Laura..... I feel the EXACT same way. When I read your post I thought... wow.... I could have written that.

My whole life I've been acting a certain way and now all of a sudden at 35 yrs old I get diagnosed borderline. Great!!! It all makes sense. And now I feel hopeless for my future. Like I'll never have a healthy relationship. and I'm just doomed in general.

So I'm Not much help... but I wanted you to know your not alone. I feel this way too. It sucks! But I guess the only thing we can do is stay in DBT therapy and work on skills to control our emotions. Seems impossible to me but others say it works. Best of luck to you!