Rumours have circulated over Houston’s sexuality for the last 30 years, with speculation that the singer had a secret relationship with her ex-assistant, Robyn Crawford.
Gay rights activist Peter Tatchell, who met Houston at a HIV support rally, has said her marriage to Bobby Brown was a guise.
Tatchell said: “It’s important to tell the truth about this aspect of her life. Whitney was happiest and at her peak in the 1980s when she was with her female partner.
“They were so loved up and joyful together. Perhaps her inability to accept and express her same-sex love contributed to her substance abuse and decline.
“She was pressured into the Bobby Brown marriage. It was a disaster. Her life started going downhill soon afterwards.”
Houston fans have responded on Twitter, and one called Tatchell a “racist f***”.
A Twitter user said to Tatchell: “Shame on you. Who are you to say if Whitney was happy with Bobby? Did you meet them? I did and they WERE happy! Grow up!”
He responded: “If Whitney was so happy with Bobby why did she turn to substance abuse?”
Houston, who was found dead after taking a cocktail of drugs and booze on Saturday, knew Crawford since she was 16 and Crawford dropped out of college to work for the star.
Crawford wrote a Valentine’s Day tribute to Houston for a U.S. magazine, which said: “I first met Whitney when I was 16 and knew right away she was special.
“Whitney was modelling and had peachy-coloured skin and didn’t look like anyone I’d ever met in New Jersey.
“I can’t believe that I’m never going to hug her or hear her laughter again.”
Brown, 43, wrote in his biography that the pair’s marriage was “doomed from the very beginning. I think we got married for all the wrong reasons. Now, I realize Whitney had a different agenda than I did when we got married.
“I believe her agenda was to clean up her image, while mine was to be loved and have children. The media was accusing her of having a bisexual relationship with her assistant, Robin [sic] Crawford. Since she was the American Sweetheart and all, that didn’t go too well with her image.
“In Whitney’s situation, the only solution was to get married and have kids. That would kill all speculation, whether it was true or not.”
Brown’s sister Tina claimed that she had seen Houston with women.
The singer spoke out about the rumours in 2000, saying: “I am a mother, not a lesbian. I am not gay.”