@hawkeye10,
It's a complicated disorder. Sometimes people stop taking their meds because they really enjoy the manic state, they are never ready for the crash. I'm not making excuses for this woman, it was stunningly dishonest, especially the fact she kept her meds at his place.
Managing BP, even if its successful, doesn't mean the individual will become a nice person. There are a lot of dishonest people who are not suffering with BP.
Since the OP was kept in the dark, and also her anger over his parents and resentment about her parents is a big red flag. She's apparently being treated for BP, but she is also very controlling, and likes playing mind games. She's trouble, and he is better off with this gal out of his life.