Yuu: Bisexual. This ones pretty easy since he has a harem of both guys and girls. There's a possibility he's pan too since he seems more attracted to personality than appearance

Mika: Yuusexual- Just kidding. He's probably just gay, but demisexual since he's known Yuu for a long time. 

Shinoa: Bisexual as well. We all know she confessed to Shikima about being in love with Yuu, but then there's the shower scene with Mitsuba-

Yoichi: He's totally gay as well. Remember that one time when he pinned Yuu (and knocked him out)? People also tend to ship him with Kimizuki and Mika as well, so there's that.

Kimizuki: Gay. Period.

Mitsuba: Honestly, I think she's a lesbian. We seem to have more Mistunoa moments than Mitsuyuu in both the anime and manga. Plus, even though she acts like a tsundere around Yuu, I don't think she's romantically attracted to him. 

Guren: Again, he too is bisexual as he has a harem with guys and girls. Especially because he seems to care a ton about Shinya (and we had so many Gurshin moments in the light novel) and was Mahiru's actual boyfriend.

Shinya: Gay. Not only does this man give off a ton of gay vibes, but his demon literally pointed out that he loves Guren.

Ferid: Gay, but asexual. Vampires are said to have no sexual desire other than blood drinking. Along with that, have you seen the way he treats Mika? This dude is totally a groomer-

Krul: Asexual and aromantic. Before you go all "but what about Ferid x Krul or Krul x Mika", she HATES Ferid. The only thing Ferid "loves" about Krul is her power. Plus, Krul treats Mika like a son, not a lover. Not to mention that she's over a thousand years old and Mika at this time of the manga is barely seventeen-

Crowley: Straight, but asexual. Again, as a vampire, he probably feels little to no sexual desire, so he's somewhere on the spectrum. However, he isn't as old as Ferid, so he may feel something. Then there was the thing between him and Horn... And I know that everyone ships him with Ferid, but I don't think he's attracted to him. Plus, Ferid and Crowley were both turned by Saito, so they're technically siblings. Think about that for a moment.

Narumi: Gay. Even though his squad is made up of both guys and girls, he doesn't seem to show interest in any of them other than Shushaku.

Mahiru: Straight. She was literally Guren's girlfriend, what other evidence do you need than that?

Asuramaru: Asexual and aromantic. I know people ship him with Yuu, but Asuramaru is as old as Krul is while Yuu is just a teenager. Along with that, the only interest he has in Yuu is his blood and desires.

Kureto: Asexual. Even though he kissed Aoi, he only did it in order to fuel his desires for Shikima.  In fact, he doesn't seem to care about romance at all.

Aoi: Straight. She has an obvious crush on Kureto.

Lacus: Gay. He seems to be kind of interested in Mika.

Rene: Asexual and aromantic. Again, he doesn't seem like the type to care about sex or romance.

Sayuri: Straight. In the manga, she said herself if Guren asked her to wear a swimsuit, she would do it without asking any questions.

Mito: Bisexual. She freaked out when Goshi asked if she would wear a swimsuit for Guren, but I also sense some bi energy coming off her. I don't know why, I just do.

Shigure: Straight but asexual. Don't really have much of a reason, it's more of a feeling.

Goshi: Straight. People call him a womanizer for a reason.