I told my Dad's wife first about my diagnoses, and she was very helpful, and broke the news to my Dad. But I wish in a way I'd waited a bit before I said anything, because my diagnoses was later refined to schizoaffective disorder, which was very disconcerting. I was able to explain it to my brother, but if my Dad found out the diagnoses had changed he'd almost certainly think I'd been lying to him, or exagerating to get attention, or something.

So my Dad and his wife think I suffer from BPII, while my brother is aware of the full diagnoses.

In a way you have to think to yourself, does the exact diagnoses matter? You're still the you you've always been, only now you have a label or a language which you can use to communicate to others how you've always been. That's actually a good thing. Explain to your parents in writing, if you have to, and don't put too much emphasis on the name of your diagnoses (since as in my case it might be redefined later.) Just let them know that you've been struggling, you took action to get help, and are now beginning to cope with the help of medical professionals.

Personally, I think you should be proud of yourself for facing up to your problems as soon as you have. I waited about twenty years before I had to admit the problem. By facing this early on in life you're really maximising your chances of making a good and affective recovery.