A clip of Tulisa performing a sex act on MC Ultra - real name Justin Edwards - leaked last month, prompting the singer to obtain a gagging order.
Plato Contostavlos admitted to the Sunday Mirror that he never approved of Edwards.
"What Justin did has really brought the family down and destroyed us in some ways. Tulisa is strong but it seriously dented her confidence. I tried to speak to her about it but she was so upset she couldn't talk. She was in bits. He has ripped her heart apart," Plato said.
"I remember the first time I met Justin. I picked Tulisa up one night from Camden and he was there. They were arguing in the street. I immediately disliked him and every time I met him after that he seemed arrogant and had little respect for me.
"I think he was just trying to piggyback on the fame of N-Dubz. But in Tulisa's eyes he was the one for her. She wanted to marry him at the time. They had even talked about having kids. She never told me why they split up but whatever happened does not excuse showing an intimate tape to the world."
Plato added: "Tulisa adores Simon Cowell. He has been extremely supportive to her and he has really stuck up for her over the sex tape stuff. I know Tulisa sees him as someone she can look up to and he thinks she is doing brilliantly on The X Factor. She is very grateful to Simon for giving her the opportunity. At least he is one man she can rely on."
Tulisa was recently spotted partying in LA with The Wanted.
Watch Tulisa Contostavlos in her video for 'Young' below: