How can the affair below be serious if contact was sporadic and sex only happened twice??

"I found out that my husband has been having an affair for 4 years on and off but with the same woman. I read all of their emails and the last time they supposedly talked, HE emailed her after finding out she had gotten a job somewhere. ( Long story, they used to work together, apparently she had stayed at home all these years.)

My husband emailed her right away after learning about it from a colleague. Wrote to her apologizing, saying he "got scared" when they were supposed to meet for sex weeks earlier and they both backed out from what I could gather.

I need opinions: if it's been happening this long, does that make it serious? NO DATES, but sex TWICE only, he has cheated before but always goes back to this one. I want to confront him, but does the situation sound serious? I cant talk to my family/friends about this yet.

But he seemed jealous going after her like that. In other emails, he was always telling her she should stay at home with her son, not work since he was little, she's married too. Then he goes back to her when she gets a job? And is this further proof? If its just sex, why would he care ? HE ALSO ASKED HER IF SHE HAD BEEN WITH SOMEONE ELSE SINCE THE LAST TIME THEY BROKE UP. (8 times that I could count.)

Is this normal in an affair or does it mean he's emotionally involved?

PLEASE DON'T TELL ME WHAT TO DO, I ALREADY KNOW I NEED TO LEAVE, SO DON'T ANSWER THAT, ONLY WHAT I ASKED. Thanks."