Should i marry my girlfriend? ?

8 years into our relationship.. i cheated on my girlfriend. I actually got involved in a relationship with the girl. I had feelings for her. This lasted 5 years. I was living a double life. Lying to them both. Knowing i had to, but was unable to make a choice. I finally chose my first girlfriend. I let the other one go . Now we have been together 15 years.. and have been working on starting A family. She recently confessed that she has been involved with another man behind my back over a year. She claims shes over him and wants to be with me.. that's why she confessed. But a month after the confession.. i discovered she was still contacting him. And lied about it. Now she claims it really is over with him.. and wants to spend her life with me. Should i trust. Her and move on with our lives ? Or is this relationship too tainted