Should I Stay or Should I GO?

2009 my husband first told me his old girlfriend was trying to make contact with him; he asked me if he should acknowledge her, I said yes because he seemed to need closure because she abruptly broke up. Turns out my husband had/has been emailing, flirting with & sexting his high school girlfriend from May 2009 for a year and a half while I was preoccupied finishing school and working. Turns out she is and is not the only flirtatious bad guy ('cause it takes 2 to tango). He admitted to me about leading her on by lying to her about meeting up with her whenever she wanted to come to our state (he then would chicken out & make some excuse in time to cancel on her). He admitted all this to me AFTER I let him know that I'd READ the almost 200 emails between them. I'm off balance & I don't know how to feel about any of this (= I don't know whether to be angry/sad/jealous); I just feel numb and whelmed (not over or under) and like these last few years will never be gotten back by either of us, but in contrast, these last 9 months BEFORE I saw those e-mails I've have been blissfully happy with him in my ignorance of their recent past. He says the emailing has stopped since before last summer, & the proof I read with my own eyes was that the 200 emails between them commenced before and even after he told her she could friend him on facebook as evidenced by the fact that I saw her name once in his pull-out chatbox on facebook this March. Obviously I don't trust him; some part of me, the undevastated part, still loves him and wants him because this was an "emailed in" past emotional affair----on his part he just fed her a pack of lies about his life, what he'd been doing/going to do, where he was going. The sexting was real, inappropriate and fantasy. The whole thing was disrespectful to me and our (supposed) relationship. All this anxiety I've been feeling is making me hurt mentally, I feel so bad. I exercise to try to stop the pain, haven't been eating much.