Should I end it?

When it comes to relationships I move very slow. I like to get to know the person first. The guy I have been dating for eight months now I was best friends with a year and half before I dated him. Everything in the relationship seemed good to me, every once in awhile we would have arguments but we forgave each other. He treats me well, spent time with me and always checked in on me. I fell in love with him. He made me feel special. But about 2 months ago I found out he was cheating on me. Throughout the entire relationship he was flirting with multiple other girls. I eventually learned he sent another girl gifts starting about three months ago and took her out on dates and even took her back to his place that was filled with a lot of my things. He had been cheating on me and lying to me. I found this out about two months ago. He was in a serious relationship with her for another three months. He keeps asking for me to stay and told me how bad it was when I stopped talking to him and that he took me for granted. I've given it time and I have been trying to work on the relationship, but I find myself to always be worried and that I feel like he is always lying. He started to do the right thing to fix things, but I'm not sure if I can continue the relationship.