Hello Misskriss. I can only relate my own experiences and some of the experiences of those close around and that may be far different from what proper medical advice may advise. The following is going to sound confusing, but I will try and give you a couple of links at the end that may help.
In regards to bipolar itself. There are 4 different types of bipolar and each type may over lap. There are also rapid cycling and mixed states, which a person may or may not suffer from as well. The illness can come on suddenly at any age, or it may take yrs to develop into a problem. Some people with bipolar never experience any symptoms until something sets it off. Like antidepressants, anxieties, stress etc. Remove what is setting it off and for a lucky few it may disappear totally.
Unfortunately bipolar tends to be a progressive illness, that is , unless it is stopped at some point we continue to get worse, not everyone, but a majority.
In regards to medication, most of us that have bipolar take medication, at least initially until it is under control. Even then a vast majority of those who remain stable in the long run continue to take medications every day. Some people take one medication, some people have to take 5-6 medications to control it. Most medications that are used to treat bipolar have short term and sometimes long term very unpleasant side effects and they are a big reason why some people won't take medication.
Believe me, even if you suggested a medication, it would be pure fluke if that medication was the one that worked. That's assuming that he has bipolar and not some other illness or combination of illnesses. It's usually a long road to find out what works.
In regards to therapy. Most really reputable therapists would either insist on the patient with bipolar having a doctor or referring them to a doctor once a diagnosis of bipolar becomes evident. Therapy alone does not help much if the person has mania as a therapist cannot prescribe medications( the exception being if the person has a long term relationship with that therapist and is able to manage their own behaviours with the limited use of medication). CBT is not known to help someone with mania unless they are really stable at the time and even then DBT (dialectical behavioural therapy) is the more preferred therapy. Unfortunately most therapists are not trained in DBT, unless they have specialized in that field. A psychologist, with a phd, may have a working knowledge of it. ( side note, a psychologist cannot prescribe medications and a psychiatrist can. In a perfect world we would have one of each , it's not a perfect world).
In regards to border line personality disorder. Just about everyone with untreated and serious bipolar will have signs of having BPD. The major difference is in treatment. Bipolar usually requires different meds and BPD most often responds better to therapy and sometimes medication. I was once diagnosed with BPD and Bipolar, once my bipolar was brought under control the signs of BPD disappeared.
In regards to tests for bipolar. One problem here is perception. A test found at
http://www.blackdoginstitute.org.au/docs/Self-testingforbipolardisorder.pdf The problem with this test is that before diagnosis I would have answered "no more than usual" for most of the questions. Had my wife given my answers for me, her answers may have been radically different, but maybe not enough to push me into the "has it category" . Doctors have better tests, but it all comes down to the same thing, how good are we at self examination and what is our own perception of ourselves and how much time the doctor is willing to spend probing.
The largest obstacle to a test for bipolar is time. Feeling really lousy or suicidal makes it easier to diagnose depression. But someone who stays up all night and accomplishes a great deal with their excess energy from short term mania, may feel that nothing is wrong, so tests will show little. Patients tend to be lousy at self examination, until the illness really affects their life so they often respond wrongly to questions. The question did you feel overly energetic means nothing to someone , we would all like to feel energetic all of the time. In all my decades of living with bipolar I've had one really good psych evaluation. Between the questionnaire that I took and the interview with a nurse and then a specialist it took about 4 hrs and that was only to confirm that I had bipolar and that I was receiving the best possible treatment for it. (I had already been diagnosed for 3 yrs at the time with bipolar)
A good psychological evaluation includes a physical , to rule out physical causes, a complete family history, a complete psychological interview, repeated several times if needed and interviews with family and loved ones to bring out inconsistencies etc. That doesn't happen very often in Canada.
Keep learning and pick your spots when to talk to him. Good Luck and Take Care. paul m
https://mooddisorders.ca/faq/bipolar-disorder