I think that there is that, but also things like straight people being like: "Oh you're bi? That's fine, then you just have to date people of the opposite gender since you're still attracted to them." Just as an example.

Sex and intimacy is by it's very nature exclusionary. Gays and lesbians not wanting to be in a emotionally intimate with a bisexual is not in itself biphobia. The only reason someone would feel it is oppression is if they feel sex and intimacy is a right and being denied those things is hate.

That being said bisexuals experience homophobia just like homosexuals. Anti same sex legislation also effects bisexuals. Bisexuals also experience a disrespect of their sexual orientation and sexual boundaries. LG often treat bisexuals as if they are in denial or not part of the community if they have an opposite sex partner, this what we call bi-erasure. Bisexuals are often made to feel like people without a community or connection. Bisexuals are often slut shamed or treated like like village bicycle. It is complicated.

One of the hardest things for human beings to do is understand others experiences and oppression.

I think a lot of biphobia stems from stereotypes attached to bisexual people within the scope of dating, yes. People have bad dating experiences and then assume all bisexual people are promiscuous cheaters or don't understand what it feels like to be bullied or discriminated against for their sexuality. The issue is, bisexual people are no more likely to cheat than gay or straight people. Having "more options" doesn't equal promiscuity, and if someone cheats then it's a measure of their character, not their sexuality.

Regarding something else I've heard people say, which is the fear that if they're in a relationship with a bisexual person, the bisexual person is going to "suddenly decide they're not gay/straight" and break up with them, I think that stems from the idea that bisexuality itself doesn't exist or isn't a sexuality with the same weight and authenticity behind it as gay or straight. Yes, there will be instances of bisexual people realizing they're not actually bisexual, but it doesn't speak for the community as a whole.

A lot of bisexual people struggle with feeling fake or without belonging. They face isolation from both the gay community and the straight community, even outside of dating. "Too straight" to relate to and socialize with the gay community and "too gay" for the straight community. If a bi person is dating a person of the opposite sex/gender, or develops a crush on a man/woman, therefore "passing" as straight, that doesn't immediately erase their same-sex attraction, and vice versa. They might have some forms of "straight privilege," socially, but this itself also adds to the erasure of their actual sexuality. They are going to have a different experience than a gay person, but they are also not having the same experience internally as a straight person by virtue of not only being attracted to the opposite sex/gender.

In terms of homophobia and discrimination, if a bisexual person exists, a homophobe is going to judge them based on their same-sex attraction. They aren't going to think, "well, they like the opposite sex/gender too, so I guess it's okay for them to be a little gay." These exist outside the realm of dating, in how the general public perceives them. In that way, they're bound by the same homophobic assumptions and stereotypes that affect gay people.

That being said, I think if someone is dating a bisexual person or is interested in them and they have concerns, communication is key (just be tactful in how you go about it.) And at the end of the day, nobody can tell you who you should date or be attracted to. If you're a lesbian who doesn't feel comfortable dating bisexual women because of previous experiences, or who feels she connects more to other lesbians, I think it's fine to have those preferences as long as we can acknowledge the larger scale of discrimination against bisexual people, and that personal experiences don't speak for the population as a whole.