Why does she keep doing this?

my current bf and his ex broke up like 11 months ago (we been together 6 and literally spend all our time together, sleep in the same bed every night etc) and since then there have been all kinds of dramas, she msg and tries calling him, he doesnt reply or answer he just wants her to go away, she threatens to send people around to bash him and even pulled the im pregnant with your baby crap telling him to answer his phone because she found out the of the baby, he told me she was lying and sure enough her friend text him saying she had been in a bad car accident and they werent sure the baby would survive... then her new bf(who she left my current bf for and was married at the time btw) msg to say they did scans and she was only 6 weeks along so it couldnt have been my bf's-tried rubbing it in etc) she left us alone for a bit, but then last week she starts up again saying she lied about all of that and she is really due in two weeks with his baby and she didnt want to admit it!! wtf!!! so now its an 11 month pregnancy!!! so i answered the phone and caught her out in all her lies... (my bf has happily shown me all her msg, hasnt tried to hide anything) then my bf sisters fiance grabbed the phone and did the same thing ( i think that pissed her off cause he never introduced her to his family and ive known them all since day one, we all go out, camping, movies parties etc, im "aunty Sarah" to his niece and nephew...which his dad says not me btw). next morning she text him saying "ha ha my bf was sitting beside me the whole time to see how you would react, lol". why does she do this?? she left him for another man!!! is she just a psycho??? this isnt teen dramas either, im 28, my man is 30