In the conversation Shelby's boyfriend states that he wants her to look like she does in her social media pictures because "that's how [he] was introduced" to her.
Shelby responds by saying that she has only gained five pounds (2kg) and asks if he is less attracted to her because of it.
He says he doesn't think so but it "will if it keeps going", topping the conversation off by telling her "you're definitely getting a beer gut babe".
The exchange was posted online last week and since then it has received over 5000 comments, mostly from people encouraging her to break up with her boyfriend.
"You need to let that person go. You are clearly a healthy weight," one user said.
"Dump him and buy a dog," another suggested.
And it appears that Shelby took the advice, with an update on Saturday saying that they had now broken up and that he "was really unhappy" after her tweet gained so much attention.
She later posted another text exchange, claiming that the post going viral actually helped her now ex-boyfriend to realise he was in the wrong.
But while most people were supportive of Shelby's decision, there were some that criticised her for posting the conversation online, claiming couples should be able to discuss delicate matters like weight.
"A couple should be able to talk freely about their thoughts and feelings. Not saying he didn't step over the line but putting him on blast on the internet maybe wasn't the greatest decision either," one person wrote.
Another added: "Do you want honesty or lies? You've asked him for his opinion, in a private convo, and he's given it to you without being horrid. You've then publicised it across the internet to shame him. Seems hugely unfair."
