Here is how the show is handling things. Over the past few months, "Corrie" had it revealed that Billy (the local vicar) was involved in a robbery and hit & run accident years before. He wasn't the driver, but didn't report the accident and a former regular (Sarah Barlow) was killed off. Mind you, this was years ago and Sarah wasn't killed by a hit & run driver at the time. But needs must, I guess.
Anyway, Billy turned his life around and became a vicar and then settled down in the same neighborhood where he had previously committed criminal acts. His life has become intricately involved with the various members of the Barlow family and he recently realized that he'd been involved with Sarah's death. He's spent the past month trying to make amends for her death with the Barlow family in different ways, but -- only through Todd's intervention -- had refrained from confessing to his involvement with her death.
Until last week... He ended up getting involved in a random near-death incident last week and confessed to his involvement in Sarah's death to her twin brother, Peter Barlow. Instead of going to the police, Peter decided to enact a revenge plan. He contacted Summer's biological grandmother and gave her enough information to demonstrate that Billy is an unfit parent. This led to a shadowy approximation of Todd swooping away with Summer for parts unknown -- hence their departure from the program and from Billy's life.
Peter then locked Billy in the trunk of his cab and hid him away out in the wilderness. His original plan was to scare Billy and ruin his life. He was going to leave Billy out in the wilderness. However... Billy stumbled and fell off a cliff on Christmas Day!!
And that's when we learned that Billy is immortal! Not really, but he somehow survived this remarkable fall -- and now he's stuck in the hospital with lots of broken bones and no clue about Todd's whereabouts.
Peter has confessed to the rest of the Barlow family so everyone -- including Adam Barlow (AKA Sarah's son, AKA Todd's law partner) -- and they have pulled ranks. Ken Barlow, the family patriarch, struck an uneasy deal with Billy in the hospital in order to protect Peter from a likely prison sentence. Billy is to tell everyone that he simply fell off the cliff and they will keep his secret about Sarah. Nobody is happy with the deal, but what's the alternative?
Of course, this secret will come out eventually. Adam is already secretly plotting revenge against Billy and Billy will be stupid enough to remain on Coronation Street instead of running as far as possible.
And that is how "Coronation Street" broke up their one set of same-sex parents on Christmas Day.