The less emotional you are, the better... . I think I should rephrase this sentence. Obviously you are emotional, it is an emotional situation. Your entire predicament is emotional. What I mean to say is that the expression of your emotion should be drama-free. BPD sufferers latch on to perceived nuances. So, you cannot control his reaction nor can you control his emotions... . just as he cannot do it to you.
I try this, but have to say that it then turns into my dBPDh telling me how "cold and emotionless" I've become. As I really have a "caretaking" personality, I have found this very difficult to get past. After a lot of work, I've come to realize that this is just another way that I've been manipulated, but would guess a lot of us fall into this trap.