I can tell you this is not specifically a "straight" issue. My friends and I have all discussed this at length (it's a long long highway between Vegas & Phoenix)

Nobody wants to get dumped or cheated on when the bisexual member of the relationship has urges for the other sex. A lot of people can't handle a 3rd person on the side. Even fewer people can handle an open relationship. It's up to you to decide what you're willing to allow in order to love this person.