Yes, I agree that printing your thread out would be a good idea and make it easier to talk about.
Have you read at all about borderline? Because what you describe sounds very much so to me. We can't diagnose of course, but it's something I've read a lot about because my BF has many of the same issues you are dealing with. I have bipolar, but couldn't understand his behavior. When I learned about borderline, it explained so much. And when I read Walking On Eggshells, I cried. It was a revelation.

Many people say that bipolar and borderline are hard to tell apart. I disagree. There are some significant differences. Maybe living under the same roof with one of each for 6 years helps me see the contrasts more(?)

Here are some key things to look for... Borderline is an ongoing state of affairs, because it plays out as reaction within relationships and other situations. The forces come from outside, then cause a variety of reactions within the person with borderline. There is a sense of having no control of one's emotions. And they can turn on a dime. This makes relationships hard as this tends to bring on chaos. There is a sense of on-going crisis (if it's not one thing, it's another and things which others would brush off, a borderline person feels they can't because their emotions are so intense). Also, there is a strong tendency to "read into" things meanings that aren't intended by the other person.

Fear of abandonment. That's a biggie. Like you said, it tends to drive people away. Attack then desperation (I hate you but don't leave me!!!) There's a lot of black and white thinking. Hate/love. All good/all bad. Middle ground is elusive.

Related to that, there is what they call idealization/devaluation. Someone will get put on a pedestal, but then does (or fails to do) something that is perceived as negative and suddenly they are considered a total villain. There's a persistant pattern of unstable, intense and tumultuous relationships.

I've seen in him too the short-lived spells of "happy and normal" you describe. They seem to happen when things are going his way (there's not as much to react to maybe?). But all it takes is one thing and boom! Right back to square one.

There is a very good description of borderline right on this site. You'll find it under "conditions" (at top of page). This takes you to a page where you'll find BPD on the lower part of the right-hand column.

Good news is that there is a therapy called DBT, and I've heard that when someone really applies themselves, it can be a huge help.

(This is already a book, but in a nutshell regarding bipolar, the troubles are episodic. Also, big shifts in energy levels, not just moods as people often seem to think.)