Why do guys lie to their side chicks even when the side chick knows about their main relationship?

Anonymous
I sadly was a side chick for to a guy for a few years when I was younger. I found out about his girlfriend after getting involved with him. I confronted him with proof that I knew. He still lied and denied his girlfriend. However, he wanted to continue a sexual relationship with me. I went along with this for awhile because I had grown attached to him... eventually I came to my senses and ended the relationship. The guy continued to pursue me and denied his girlfriend despite my always being direct with him and providing proof that he was in a relationship.

Why did he continue to try and lie to me? I'm just curious because he reached out to me again despite my ongoing ignoring of him.
Why do guys lie to their side chicks even when the side chick knows about their main relationship?
9 Opinion