The guard told him a complaint had been made about the couple by another shopper.
They’d been holding hands while buying food after work.
“He waited for us to finish paying and he then beckoned us out of the store with his finger and said, ‘Follow me guys,'” Thomas tells Newsbeat.
“I’m humiliated, we were stood in the street.
“He said he’d taken us outside so as not to embarrass us in front of the other customers.
“Well, I’m not embarrassed, I’m not ashamed – I have nothing to be ashamed of. You’re not saving my dignity by taking me outside, you’re just exposing your small mindedness.”
Thomas now says he wants better education and training for security staff who have to deal with similar situations.
“All security guards in bars, restaurants, in nightclubs, supermarkets – they are the frontline for situations like this,” he says.
“They need to have the appropriate diversity training so they are able to handle these unique situations with a bit more respect and in a more official way than he did.
“From this security guard’s point of view, he lacked the training and the experience to deal with the situation and it was his naivety that was at fault here, not any kind of prejudice.”
Sainsbury’s has said sorry to Thomas and his boyfriend, assuring customers that they are an “inclusive retailer”.
“We sincerely apologise to Thomas and Josh,” Sainsbury’s says in an official statement.
“We are an inclusive retailer and employer and do not tolerate discrimination in our stores. We will take appropriate action once we’ve concluded our investigation with our security contractor.”
Thomas says he’s satisfied with the response, but hopes the supermarket chain will be more open about steps taken to prevent similar incidents in stores.
“What they need to do now is push the point that they are educating staff, there is a programme in place and there is a procedure of how to deal with these situations,” he says.
“It’s more about transparency on how they employ security staff, how they educate staff and what they’re going to do, what steps they’re going to put in place now to make sure this doesn’t happen again.”
However, he says he’s less impressed with the compensation he was offered by Sainsbury’s – a £10 gift card.
“It’s not about the money, but that’s become more of an insult now,” he says. “[It’s like they’re saying] ‘here’s a tenner towards homophobia, sorry about that.'”