i have often heard it described as walking on eggshells. in fact there is a book by that very same name that is a guidebook of sorts to living with someone with bpd. if you are interested in the symptoms, google bpd in the dsm5. there is often difficulty in relationships. you can be their best friend one day and the next day you are at the top of their shitlist without even know why. they can be very insecure in relationships due to a fear of abandonment. that is all i have off the top of my head right now. my sister was bpd. she was extremely had to live with. i often had nightmares of her hunting me down to kill me she was so volitile. but she could also be very sweet and loving.