I thought I needed to know - please help

I was nc for a while with my sociopathic narc, nc gave me the clarity to see that certain things were not adding up such as an illness he told me he had. So, I did what I do best -I made a plan. I bought a GPS tracker put it on his car and broke nc to figure out his lies. So, yes, I was right he was in fact lying and telling me he was getting chemo. What I also learned was "chemo" was code for going to the track. He was working far less than I was being told and spending that time at the track instead. He has an apartment in a completely different town than where he told me was living. Well, tonight was the icing on the cake - I have come to see that he never goes to his apartment because he has been living with the girl he told me he broke up with almost 3 years ago. I couldn't take it and confronted him on this little detail. He, of course, lied. He told me he was so disappointed in me for not really knowing him the way he had hoped I did. He said he was angry with me and that I was selfish - how could I accuse him of this when he needed to focus on his health. I am so screwed up over this right now. A lesson in why we should never break nc.

Why did he tell me he broke up with her in the first place? I am married. Was it to have power over me? He used to play the married card and break up with me all the time. I am dying to confront him on everything else but know it will be futile. Please help me understand that for 3 years not only was I with a raging narcissist but a full-fledged lying psychopath. Absolutely everything was a lie. It is devastating.