Judging by his actions so far
I think he's going to tell his mum/family and also tell them they have no say in it and accept it
I also think he doesn't want to come back and work it out, your dd is 15 he's not worried about young kids being caught up in this.
He has t been at all bothered about getting caught or trying to hide his deceit, I think he's glad you know and he's barely missed a beat since then
I wouldn't be surprised if he hasn't already got his ducks in a row, wants a divorce and move forward as quickly a possible. His sorry it hurts says it all really, his disconnected from all of it, telling his family is just going to be a chat over a cuppa, a look after yourself from mum and business as usual.
World I'm so sorry this is happening to you, I think only do things that benefit you, and try to avoid all emotional wrangling with him, because I don't feel he cares enough to give you an emotional response back.
Work out your practicalities, and what you need financially etc and take support where ever you can find it.
💐