As per my knowledge, one of the causes of BPD are invalidation of a child's feelings. They learn that their opinions are wrong through their abusive parents and/or partner

Now, I don't want to invalidate feelings of an adult person with BPD, but when they're splitting, there seem to be 2 options. 

Either accept whatever they are accusing you of. such as "you are a sexual predator, you were planning something against me" etc

Or you invalidate their feeling by saying no it's not true

How do I solve this issue?