Chelsea* feels disgusted by her long-term partner, Ashley*, after he revealed a family secret.

"I’ve been with my boyfriend for over five years," Chelsea shared to Reddit, who was originally looking forward to going on holiday with Ashley's family.

"We’re all on a family trip together right now (his mum, dad, stepbrother, stepsister, and a bunch of his other relatives)," Chelsea began. "And this is the second time I’m meeting his stepsister."

Chelsea continued: "He was absolutely wasted last night and I was telling him how much I like his stepsister.

"[Ashley] continued by telling me I should dress like her, which I thought was a little strange.

"Then I said, 'sounds like you have a thing for your sister; and he came out and told me over 15 years ago, him and her slept together many times."

"He kept mentioning it last night almost as if he was proud of what he did," Chelsea revealed. "Repulsive."

Chelsea said: "Apparently no one knows [about it] in his family, and only his best friend knows about what happened.

"Now I honestly can barely look at him, I feel so beyond disgusted and am second-guessing our entire relationship."

Chelsea added: "We have three more days on this family vacation and I want to book an earlier flight and go home."

Feeling "torn" about her next steps, Chelsea asked the people of Reddit if she was overreacting.

"I would love some insight from others," said Chelsea. "I feel shallow for judging him this negatively about the situation..."

Many took to Reddit to advise Chelsea to "book the flight home" and to leave him.

Ok-Willow-9145 stated: "This is totally abnormal. It’s especially creepy that he asked you to dress like the family member he was sleeping with. Go home."

Although Tiacalypso said: "Stepsister isn't a genetic sister." Southcoastal confirmed "it's not incest, but it's still not socially right".

Southcoastal added: "The real ick is the fact that he wants you to dress like her. Sounds like he still has a thing for her. Maybe she broke it off and he’s never really got over her."

*Names have been changed.