October is Black History Month in Britain – a wonderful celebration of the huge, important and valuable contribution that black people have made to humanity and to popular culture.

It is also worth celebrating that many leading black icons have been lesbian, gay, bisexual or transgender (LGBT), most notably the US black liberation hero Malcolm X. Other prominent black LGBTs include jazz singer Billie Holiday, author and civil rights activist James Baldwin, soul singer-songwriter Luther Vandross, blues singer Bessie Smith, poet and short story writer Langston Hughes, singer Johnny Mathis, novelist Alice Walker, civil rights activist and organiser of the 1963 March on Washington Bayard Rustin, blues singer Ma Rainey, dancer and choreographer Alvin Ailey, actress, singer and dancer Josephine Baker, Olympic diving gold medallist Greg Louganis, singer and songwriter Little Richard, political activist and philosopher Angela Davis, singer-songwriter Tracy Chapman and drag performer and singer RuPaul.

Few of these prominent black LGBT achievers are listed on the most comprehensive UK Black History Month website, which hosts biographies of notable black men and women. In the section on people, only Davis is mentioned and her lesbianism is not acknowledged. The website fails to identify the vast majority of black public and historical figures who are LGBT. The Official Guide to Black History Month UK is equally remiss. Why these omissions? Black people are not one homogenous heterosexual mass. Where is the recognition of sexual diversity within the black communities and black history?

In contrast, LGBT History Month, which takes place in the UK in February, devotes a whole section of its website to the lives of leading black LGBT people and links to the websites for Black History Month. Disappointingly, this solidarity is not reciprocated. On the Black History Month websites I could not find a LGBT section or a LGBT History Month link.

Perhaps it is unintentional but Black History Month sometimes feels like Straight Black History Month. Famous black LGBT people are not acknowledged and celebrated. Either their contribution to black history and culture is ignored or their sexuality is airbrushed out of their biographies.

A good example of this neglect is the denialism surrounding the bisexuality of one of the greatest modern black liberation heroes: Malcolm X. The lack of recognition is perhaps not surprising, given that some of his family and many black activists have made strenuous efforts to deny his same-sex relationships and suppress recognition of the full spectrum of his sexuality.

Why the cover-up? So what if Malcolm X was bisexual? Does this diminish his reputation and achievements? Of course not. Whether he was gay, straight or bisexual should not matter. His stature remains, regardless of his sexual orientation. Yet many of the people who revere him seem reluctant to accept that their hero, and mine, was bisexual.

Malcolm X's bisexuality is more than just a question of truth and historical fact. There has never been any black person of similar global prominence and recognition who has been publicly known to be gay or bisexual. Young black lesbian, gay and bisexual people can, like their white counterparts, often feel isolated, guilty and insecure about their sexuality. They could benefit from positive, high-achieving role models, to give them confidence and inspiration. Who better than Malcolm X? He inspired my human rights activism and was a trailblazer in the black freedom struggle. He can inspire other LGBT people too.

Right now, there is not a single living black person who is a worldwide household name and who is also openly gay. That's why the issue of Malcolm X's sexuality is so important. Having an internationally renowned gay or bisexual black icon would do much to help challenge homophobia, especially in the black communities and particularly in Africa and the Caribbean where homosexuality and bisexuality are often dismissed as a "white man's disease".

So what is the evidence for Malcolm X's bisexual orientation? Most people remember him as the foremost US black nationalist leader of the 1960s. Despite the downsides of his anti-white rhetoric, black separatism and religious superstition, he was America's leading spokesperson for black consciousness, pride and self-help. He spoke with fierce eloquence and defiance for black upliftment and freedom.

Malcolm's complex, changing sexuality was never part of the narrative of his life until the publication of Bruce Perry's acclaimed biography, Malcolm – The Life of a Man Who Changed Black America. Perry is a great admirer and defender of Malcolm X, but not an uncritical one. He wrote the facts, based on interviews with over 420 people who knew Malcolm personally at various stages in his life, from childhood to his tragic assassination in 1965. His book is not a hatchet job, as some black critics claim, it is the exact opposite. Perry presents an honest, rounded story of Malcolm's life and achievements which, in my opinion, is far more moving and humane than the better known but somewhat hagiographic The Autobiography of Malcolm X: As Told To Alex Haley.

Based on interviews with Malcolm's closest boyhood and adult friends, Perry suggests the US black liberation leader was not as solidly heterosexual as his Nation of Islam colleagues and black nationalist acolytes have always claimed. While Perry did not make Malcolm's sexuality a big part of his biography – in fact, it is a very minor aspect – he did not shy away from writing about what he heard in his many interviews.

He documents Malcolm's many same-sex relations and his activities as a male sex worker, which spanned at least a 10-year period, from his mid-teens to his 20s, as I described in some detail in a previous article for the Guardian. Although Malcolm later married and, as far as we know, abandoned sex with men, his earlier same-sex relations suggest that he was bisexual rather than heterosexual. Abstaining from gay sex after his marriage does not change the fundamentals of his sexual orientation and does not mean that he was wholly straight.

Towards the end of his life, Malcolm's ideas were evolving in new directions. Politically, he gravitated leftwards. Faith-wise, after his trip to Mecca, he began to embrace a non-racial mainstream Islam. His mind was becoming open to new ideas and values.

Had he not been murdered in 1965, Malcolm might have eventually, like Huey Newton of the Black Panthers and the black power leader Angela Davis, embraced the lesbian and gay liberation movement as part of the struggle for human emancipation. Instead, to serve their homophobic political agenda, for over half a century the Nation of Islam and many black nationalists have suppressed knowledge of Malcolm's same-sex relations. It is now time for Black History Month to speak the truth. Malcolm X was bisexual. Get over it.