@Hels20 because Becky made it clear to her mum that he'd raped her (even if she didn't say the words specifically) & she couldn't cope with the baby who was the product of that rape, hence killing herself.
Catherine keeping Ryan led to her and Becky's dad splitting up as he couldn't deal with Ryan either and nor could her brother. This is also why they were barely in Ryan's life when he was little and throughout series one & why Becky's dad apologised to Catherine in the last episode for leaving her to deal with Ryan alone.
It's all so clear cut to me, that I'm surprised others see it differently (other than TLR being so good looking , especially in series one, that people are trying to see innocence even when it's so blatantly not there).