Cheryl was part of a big machine on the X Factor, had minimal contact with Liam and was probably never alone with him. He was one of many faces as part of a job she had for about three months and that was it. They probably had no contact for years.
She didn't get him a job, she didn't give him special access to anything and didn't treat him any differently to anyone else. He wasn't penniless.
He was about 23 and worth millions when they got together. Not just turned 18.
I don't even like Cheryl that much but it's nonsense to compare these two situations.