Broadchurch: The Sandbrook Suspects - Cate Gillespie

Cate's Background
Cate is mum to 12 year old murder victim Pippa and aunt to missing 19 year old Lisa Newbury.
Her marriage to Pippa's father Ricky has collapsed following the death of their daughter.
Cate is rarely seen without a glass of wine in her hand.
She appears to have been involved in a relationship with her next door neighbour Lee Ashworth.
Lee later stood trial for the murder of Pippa.
Her missing niece Lisa told Claire Ripley that she hated her aunt.

An Affair With Lee
It seems as though Cate was involved in an affair with her next door neighbour Lee Ashworth.
Although Lee denies any relationship with Cate when quizzed by Alec, a flashback scene reveals otherwise, showing Lee pressing Cate in to a doorway as she puts a finger to his lips to keep him quiet until Pippa has left the house.

Meanwhile Lee's wife Claire is happy to admit to Ellie that Lee is a flirt and that other women are attracted to him, but won't admit that there was anything going on between him and Cate despite flashbacks showing that Claire was bitterly watching them from the house as they flirted in the back garden. She was even joined by Lisa Newbury who watched alongside Claire and told her she hated her aunt.
Claire tells Ellie "He was never interested in her. He was never looking to go older..younger maybe, but not Cate's age."

Drowning Her Sorrows
Cate is rarely seen without a glass of wine in her hand and Ellie and Alec assume she's struggling to cope with the grief of losing her daughter, but Claire Ripley tells Ellie that Cate was always drinking even before Pippa's death saying: "Claire: Well..I don't want to speak ill of her, not after everything she's been through, but she always had a posh glass of wine in her hand and made sure we knew it was expensive..Maybe it was because we were renting off them but I just always felt she was looking down on us, well me, Lee, she just flirted with. But everyone flirts with Lee and he just flirts right back."

Ricky also tells Ellie that on the night the girls went missing he was looking after Cate because she was "pissed".

Difficult Relationships With Her Family
Despite all they've suffered and been through together there certainly doesn't appear to be any love lost between Cate and Ricky, their relationship has ended since Pippa's death and they have no time for one another. It's a stark contrast to the relationship between Alec and his ex wife Tess, who despite leaving him still obviously thinks fondly of him and cares about him. Exactly what is it that's made Cate and Ricky appear to hate one another so much?

And it's not just Ricky who Cate seems to have trouble with. Her missing niece Lisa was also not a fan, with the teen confiding in Claire that she hated her aunt Cate. Why would Lisa hate Cate?
A flashback showed us Lisa and Lee smiling flirtatiously at one another as Lisa gazed at him from a window of Cate's house. The smiles soon stopped when Cate came to see what the girl was looking at.
Were they jealous of one another or in a battle for Lee's attentions?

Changing Her Story
Ricky and Cate had a solid alibi for the night the girls went missing, they were at a friend's wedding and staying over night at a hotel. This ruled them out of ever being considered as suspects in the girl's disappearance,but when Alec travels back to Sandbrook to let Cate know that Lee is back in the UK, she changes her story and claims that she wasn't with him all night and that he had sneaked off for sex with one of the bridesmaids, not only this but she says that he was also seeing their next door neighbour Claire Ripley too.
Why has Cate suddenly decided to tell Alec this?