Hi Chances
I can relate so much to your post. As you said, sometimes our pwBPDs explode right before going to some event because they really don't want to go, and they agreed because it's the socially acceptable thing to do. I find this to be true of my uBPDh too.
What I sometimes do now is that:
1. Don't tell him about that until nearer the event, so he won't have so much time to worry about it and have emotions brewing up.
2. Tell him in advance, discuss whether he would like to go, etc. (of course won't work if he isn't the discussing type... .)
3. Tell him we are both invite to xyz, I would like to go, it is ok whether he wants to go or not. Then, even if he said yes, or no, he may still blow up before leaving/ before you leave. Not to encourage stepping on eggshells, but during that fragile time it is best to be more validating to him, realise that he may not want to go 100% and say it's ok if he backs out. But stick to your own decision. If you've decided you will go with or without him, this is what you will do.
Good luck and yes, do read the Lessons on the right and practise them!