There is a difference between someone who is Bi-curious and someone who is Bisexual. Learn the difference.
Bisexual: Someone who knows what they want. They like people of both genders.
Bi-curious: Someone who is unsure of what they want. They may use you to find out.
Yes, bisexuals and bi-curious people are capable of cheating. You know who else is capable of cheating? Gay guys, lesbians, and heterosexuals. You don't understand them. That's fine. But that doesn't make it okay for you to treat bisexuals like they don't belong. If you support LGBT, then you shouldn't exclude the bisexuals.
Are you gay or lesbian, and are tired of heterosexuals assuming all of you are the same, that you like everyone of the same gender? Then don't be a hypocrite and do the same damn thing to a bisexual, with "You're just confused" "You're a slut" and "You're straight when you get married to a guy."
I'm a lesbian, and I support you. I have a lot of respect for bisexuals who are loyal. Who are often accused of things they've never done. You deserve better than what you are getting.
To all the lesbians and gay people who are being prejudice assholes, you are no different than the heterosexual haters. I'm disappointed in you.