Yuck. I've so been here. I suspected something was going on w/ my H off & on over the course of 3-4 months. I kept quiet until I found something concrete... him emailing back & forth w/ him mentioning meeting at a hotel & various other flirtatious comments. That same night I also found a picture of her on his phone. I confronted him then but he continued it up for 2 more weeks before I found more emails that showed me the affair was continuing. Then I confronted again & he was scared at this point & he suggested counseling & said he would definitely end it.
So I guess I would say get concrete evidence & then proceed? I think if I had only had flirtatious emails, we would have not gotten into counseling & he would not have officially ended it with her.
Sorry you are in this spot... it is a bad place to be.
T: 14 M: 12 D: 9 S: 6 BD: 2/18/15 (H affair) Working on marriage: 3/12/15-6/11/15 Broken Trust (my error): 6/11/15 H ring off: 7/6/15; Comm w/ OW confirmed 7/13/15 H wants to work on fixing things: 7/21/15