In the newest episode of Doctor Who there is a group of 2nd century group of roman soldiers. One of them is gay, but the others all appear to be bisexual. Is that based on any historical accuracy or freely invented? How was homosexuality viewed during that time?
Asking whether "bisexuality" or "homosexuality" occurred is a misnomer when talking about a culture other than modern Western society. People in Ancient Rome didn't think in terms of sexuality, but rather in terms of sex acts. This means that they might associate an individual with having a preference for the same sex, but I'm not sure they considered it a part of identity the way we do now.
When asking about same-sex acts in Ancient Rome, I can say that people were less concerned with heteronormative sex than people in Europe post-Christianity. The Greeks were noted pederasts (having a relationship between an older man (30s or older) and a younger man, perhaps a teenager) and for this reason, they were sometimes the butt (get it?) of Roman jokes. However, for all that, from what we understand, male homoeroticism was largely viewed neutrally, taking the stance that it was permissible in private but not in public (and certainly not at the expense of losing their patrimony). They considered male same-sex relationships from the standpoint of "active" and "passive" partners; that is, the penetrator and the penetrated. This conception makes physics sense when talking about male/female and male/male sex acts, but it doesn't quite hold up for women.
The only writings we have about female homoeroticism are written by men, and to be honest, speaking as someone who is bisexual and has had lesbian sex, their beliefs about how two women can have sex are not so different from many modern opinions. Male authors like Lucian and Martial assign active and passive roles to their female subjects, assuming that one must penetrate the other in order for the women to get off. They also seem to think scissoring is the most effective way for women to have sex with each other, and often they assume that one of those women has an abnormally large clitoris (Martial refers to this in Epigram 1.91, I believe. I can link it if interested, but I'm not at my computer at the moment).
Sum and substance: male authors in Ancient Rome did not hate male homoeroticism, but they also didn't make it public. Also, they can only call something sex where someone is being penetrated or there is genital-genital contact. This even extends to cunnilingus, which men considers emasculating to perform on a woman.