My ex wife started acting more distant, sex stopped and she was always on her phone talking to her friend. It started out of nowhere and like you I used to try and help as much as possible with kids and do nice things for her. I also worked 2 jobs to pay for everything as she wasn't working. She had chosen not to return to work after our first child was born about 5 years prior.

Anyway, turned out she had renamed some guys number to get friends name and was messaging him. When she was going to her friends house for a chat and a wine, she was really going to hotels with this guy.

There were other signs, always on her phone, buying underwear that in never got to see, more attention to get appearance, she also decided out of the blue she wanted a coil fitted.

This was about 6 years ago and it was a really dark year following me figuring out out but I'm out the other side. If you are unfortunately about to go through that, keep in touch with friends, stay away from alcohol and remember, it gets better.