I think with BPD it is not so much a void of feeling it is the opposite: too much feeling and no healthy way to cope with the intensity of their feelings. Their resulting behaviors may, on the surface, seem like they have no feelings but the last thing we can say about BPDs is that they have no feelings.
Yes, it is very sad, painful and lonely for many of them.
Sorry I don't mean no feeling at all, they have plently of feeling about themselves, I mean no feeling for OTHERS, no passions, no emotions about anything outside of how 'objects' can benefit them.
Upon the realisation that my ex didn't really have care for anyone, and also realised she didn't really have care for anything either, her only 'interest' was cooking, which seemed to give her constant anxiety anyway, the only reason it seemed to me she had this interest was because it was another way of keeping men on a hook.