infidelity at it's finest

So me and my husband have been married for 10 yrs. He recently had an affair with a younger woman at his job who suggested he leave his family and be with her. (He showed me the messages) He told me it only happened twice and he regrets he ever did it. I was so hurt and I vowed that I would not stay in this kind of relationship. I decided to move on, but he really wants to work on us because we were best friends for years before we ever hooked up. I don't want to loose my family nor my best friend , but I don't think i can ever trust him the same again. How can I ever give my all to someone I don't trust? I'm so confused. Need advice, Help!