I'm a person.
A person can fall in love.
Whether a person "ought" to fall in love with anyone else... is a foolish question. People fall in love; as one poster said, it happens to us, we don't decide.
So the first premise in this thread has to be that gays can fall in love with bis, and bis with gays, and that's no different than a gay falling in love with a gay, or a straight falling in love with a chick -- it's a person falling in love with a person, and to make any distinction in there other than "person" is bigotry.
I am a guy.
I have a dick; I also have a heart.
My dick is often attracted where my heart isn't, or even can't be. My heart is sometimes attracted where my dick isn't interested at all.
The one attraction we call "lust"; the other we call (not always accurately) "love". There are different requirements for the two. Lust often hungers for anything that will feel pleasant; sometimes lust can only hunger where there is love.
If you believe that it's okay for a guy to satisfy his lust with another guy, then you have to grant that it's just as okay for him to satisfy that lust with a chick -- otherwise you're sexist. Remember it's really a person satisfying his lust with another person; beyond that is irrelevant -- you may as well say black should only date black, short should only date short, or any other secondary phenomenon about a person.
There is an emotion we call "revulsion", or "disgust".
Some guys find pussy disgusting. Most don't.
Most guys find dick disgusting -- some don't.
Some guys don't think dick or pussy are disgusting, but like both.
A guy who finds pussy disgusting may transfer that sense of disgust to a guy who enjoys pussy... and discriminate on that basis. It's no difference than discriminating against people who are fat, or old, or tall, or albino.
Is it okay to discriminate? Sure -- but don't universalize it. Admit, "I find it disgusting to touch a man whose dick enjoys pussy", but don't say, "Guys who enjoy pussy are disgusting." Say, "I can't bring myself to kiss a guy who's eaten a chick out", but don't say, "Guys who eat chicks out are disgusting".
And remember that falling in love doesn't necessarily follow your own lust or disgust. It grabs your heart and takes you.
When it strikes, you may have to unlearn some disgust, to get rid of your revulsion. Maybe you'll discover, too late, that you can't, and your true love, The One, will vanish, gone -- and it will be your fault.
The time to learn tolerance and acceptance is not when love strikes; the time is now. If you think, "I could never fall in love with that kind of person", you may be writing off the most profound relationship ever to come your way. The time to tear down walls is now, before they bring on a disaster beyond your greatest fears
And if that moment never comes, you will have a treasure for your efforts anyway: the world will be a wider place, your heart will be larger.