Hey, thanks for posting on this forum. You've made a clear indication that you're genuinely concerned for your relationship, I will tell you what I think, but please - only take it with a grain of salt because in this life, "There is NO right way to handle any situation / circumstance."
I'm pleased to hear that you've both managed to be together thus far. I'm assuming you've known eachother for quite some time, which to be honest - should make it easier for the two of you to remain compassionate for one another, even when the fights and arguments break out.
The important thing (From my point of view) is that you both recognize and respect one another for your illnesses. Ironically, that may make things easier for you to remain respectful of one another, even if and when; the respect is not deserved.
The trouble with Borderline, (I have it) is that relationships are extremely hard to maintain. (at least for me they are) Take into account that most Borderline people manage better relationships with people who are stabile and grounded, who have solid foundations to depend on when life hits them like a sack of bricks. You not only have to manage you're own issues, you've also got to take on some of your boy friend's issues - and that becomes extremely hard to cope with; especially for people like you and I. (Respectfully said of course)
Personally, I've been in a relationship with a Borderline girl. (Both myself and her were borderline) And to tell you the truth - things went downhill FAST. The first mistake I made was to let my abandonement issues and emotions control my behavior - which ended up pushing me to making late night phone calls in tears and asking for assurances that she would never leave me. She recognized the symptoms fast; as she too was capable of becoming similarly tainted with pain... Only problem was, I went to her for help, when really - I should have gone to my therapist. OR, to a support system where I could recieve some helpful non - judgemental objectivity on my behavior and the reality of the situation. I ended up pushing her away because of my attempts at preventing my fears of abandoment. If only I would have been able to control my emotions and ground, (center myself and try NOT to make any decisions when the extreme emotions come) I would have still been in the relationship with her. At least - I think I would be, but who knows; perhaps she would have done the same to me if I hadn't of done it to her first...
All-in-all; it CAN be done. I would say the longer you're in the relationship - the better your chances of making it last. The important thing to remember is that your emotions WILL pass, even when they are at their most extreme... My advice to you is - just let things happen on their own. Stay in the present, don't worry too much about the breakup, don't worry too much about making things work. Just be in the present moment - and accept anything that comes your way, one step at a time.
No sense worrying about something so much that you ironically end up making it happen in a desperate attempt to prevent it. (Borderline people ironically push those closest to them away, especially when they try so hard to pull them closer)
As for your boyfriend, if he is bipolar; I know alot about it and I gotta say that it's a whole 'nother world of pain. Unfortunately, and I'm NOT discounting or invalidating reasons for his mood problems, I would say that bipolar disorder has more to do with brain chemistry than with the PAST. I personally believe that Borderline has more to do with the past coming back to haunt us... I suppose the good thing about Borderline - is most times; atleast after the initial shocking emotions and episodes of compulsive behaviors - it is quite predictable. Bipolar, however; is often times unmotivated and extremely unpredictable - which - can and does come as slightly more intimidating to those who lack compassion for the mentally ill.
Now, if you can both do eachother a favor - and maintain your own friends and support systems outside of shared friends and relationships; you should be able to return to eachothers arms if and when fights should break out. Don't rely too much on him, unfortunately (And not to spark emotions in you) the fact that you came to this website and asked for advice gives me the idea that you've already contemplated the possiblity of breaking up with him... I'm assuming it would be for the best - which I'll trust that you can personally remain objective about.
Perhaps buying eachother books on eachother's illnesses. Making it a, "joke," (mutually understood of course) that you're both mentally ill and you've both got things about eachother that you don't like, but cannot control. (At least cannot control to a certain extent) My idea would be that both of you read a book on eachother's illnesses to gain some insight. Perhaps you could even read your book on Borderline first, and highlight parts that really stick out to YOU - and could be beneficial for your boyfriend to pay specific attention to. It's really a simple thing to do.
The important thing to remember is - that neither of you likes to be stigmatized. And although you both have illnesses, neither of you IS your illness... You've just been afflicted with a set of symptoms that are unfortunately categorized and labelled as such in the DSM-IV... You are both lovely people - as are all people; just remember that in times of trouble - you're ability to remain calm will help to neutralize high-energy situations from growing more intense.
Hope you got something out of this. I must apologize that I rambled, I will look back on here when I have more time, I am just about to go to sleep for work.