Let me begin this by saying that I've always thought I was bisexual...but recently, I've begun to think that maybe this isn't true.
I've been dating this girl for awhile, and she seems perfect. She's kind, cute, thoughtful, and we have similar interests. At first, I was so happy to be with her. But recently, I've felt myself getting annoyed with her...because she's not a guy?! I don't understand these feelings myself, but I've noticed thinking things like 'if only she was a guy' and 'I'm embarrassed to be with her' and things like this.
I don't know what to do, because sometimes I feel truly happy with her, but sometimes I just want to break up. I have no one to talk to about this, because everyone will have their own goals in mind when they hear about how I feel.
In addition to this, I have an illness that makes me unable to understand reality properly.
I have no idea what to do...can anyone offer any advice?

Wow. You got it rough. Well I will give you my advice and even my ears. I think you should talk it with her. If she is really that amazing to you then she might know what to do. It also might be a test. If she rejects you then she is not the one but if she helps you she might be the one or a really good friend. Also even if you have a illness talk to yourself. Soul digging you should call it. And if that doesn't work talk to me. I will keep giving you advice and support. You part of the the dollars!!

I am not good with advices but, i was reading a novel amd a character just said the same thing you said. As you said you "beliebed" that you are bisexual which mean you aren't, because that is something you choose for yourself then you believe it, in my opinion if you're uncomfortable (or even started to feel disgusting) you should take some time to clear yput mind and mihht also break up, they way you say it, it just sound like you love her as a friend not a partner.
Still take your time and think about what you really want

1- Determine if you are frustrated with your current situation because of her gender or because of the expectations society puts upon your choice of relationship.

2- Do you think it would make you and the girl happier to break up? If yes, decide how to best go ahead.

3- There are many forms of attractions (aesthetic, romantic, sexual and sensual) and bisexuality is not defined on whether or not you are necessarily "happy" with the person.

If you are concerned with labels, just check the definitions of the terms stated above and see how they apply to you. Otherwise, do not feel pressured in labeling yourself. It can be a somewhat restrictive procedure on your understanding of human relations.

4- Do be honest with them and yourself.

I wish you the best of luck.