Today I (29M) found out my dad could be having a 10 year affair. How do I navigate this?

This is my first real post. I'm still trying to process this reality. My mum (58F) and dad (63M) have been married for 30+ years. Around 15 years ago, my dad moved abroad to for business as he wasn't making enough money to support the family. He would still come back to see us twice a year and stay for weeks when he does. My siblings and I have grown to normalise this situation. Throughout this time, my parents still remain married, text/call multiple times a day and my mum have plans in the near future to move to where my dad stays. Nowadays, his business has taken off now and he can basically retire.

For context, I am 29M. Around 8 years ago when I was younger, I spent a summer visiting my dad. I noticed he was messaging a lot to somebody and I snooped and found all sorts of messages of a loving and sexual nature (not to my mum). I was a huge loser at the time and remember crying all night and I couldn't confront him. I was terrified of thinking about it and my mind has done a great job of blanking it out mostly to this day. I have a lot of regret of not being braver but I worry about the consequences of confronting him. To this day I just kind of hoped this relationship would just be a fling/go away.

Fast forward to yesterday, I flew over to briefly visit and spend time with my dad. I needed to use a computer for remote-working and so he let me use his PC. Whilst doing my work that day I noticed his WhatsApp is linked to the computer and I would get involuntary message previews. Most have been work related but I couldn't help but notice a strange name pop up. It was short and cryptic with 2 letters. It also had "disappearing messages" next to the chat which was suspicious. I had a feeling of dread throughout the day thinking what if he is still having an affair with that woman. It is the worst feeling as I feel responsible for not doing anything 8 years ago while it would have been relatively fresher. My curiousity got the better of me and I opened the messages confirming my suspicions that he was having an affair. I could only see the last 24 hours of messages but he used the word "darling" many times to address her and talked about me being around very casually as well as what my dad and I did that day which made me a bit sick.

It’s 3am. I plan on finding out who this person is tomorrow. I have a suspicion it is somebody he works with (and I've met a few times) which makes me even more sick.

I feel like I need to confront him this time. I feel the worst for my mum as she is the kindest person in the world and I feel like I've let her down. How do I navigate this? It might sound selfish but if my dad promises to stop his affair, I would consider sweeping this under the rug.