Psycho Inlaws

yarrow sun seems to know what is going on here. BPD indeed, I totally agree.

Your bf doesn't need to "confront" her, but he does need to let her know there are and will be ground rules. Whether that be that she has to call before she comes over, or that he will not tolerate ill talk about you, or that she needs to keep her opinions to herself, or that ALL contacts with her will be made at YOUR own house. (OMG, he isn't living with her, still is he? If so, this will make this even more difficult. If you and he are living together, have all contacts with her on YOUR turf, and that will even out the playing field just a little bit.)

Letting someone know where they stand is good. No reason he has to "confront" her, accuse her ect. BPDs love this and it will only add fuel to her fire.

Do what Yarrow Sun said and do some reading on Borderline Personality and Boundries. If yours are well defined, it is more difficult for them to get in your space.