You made the right choice in breaking things off, and you definitely made the right choice in not buying that house - which would essentially create a financial albatross around your neck. But I don't think there's anything wrong with open relationships in general. The problem here is that it wasn't something that both parties wanted, so it was never going to work.
To clarify, is she saying that because she is bi-sexual, she needs to have sex with both men and women in order to be fully satisfied? And that further, her attraction for men is completely satisfied by her relationship with you, and therefore your attraction for women should be completely satisfied by her - ergo, the only outside sexual experiences either of you are allowed to have would be of a homosexual nature?
As a bi-sexual person, this comes off as a total crock of shit. Whether you're gay, straight, or bi, if you choose to be in a monogamous relationship, you have to give up on all the other potential sexual partners you could have had, regardless of their gender. Just because bi-sexuals have a larger "pool" of potential partners to choose from doesn't mean we don't make the exact same choice if we choose to be monogamous. Her claiming that her attraction for women must be fulfilled is simply her using stereotypes about bi-sexuals and promiscuity to justify her unwillingness to commit. If she wants to be open, she should come out and say it and not use her bi-sexuality as an excuse. If she's not comfortable with you sleeping with women, she needs to be honest about that as well and simply acknowledge that she's applying a double standard.