First, your paragraph on substances is what addicts say. I am a recovering alcoholic so I can spot that a mile away. But I'm done with that for you because a person has to want to get clean. I know that from experience.
As far as her denying there's another person, THEY ALL SAY THAT. Even in the face of undeniable evidence they will deny. They will deny until they are ready to go public with their new person. So the fact that she's denying it means nothing.
Finally, how long to wait? Well first, 9 months isn't long. Sometimes these situations go on for years. What you have to decide is how long you want to wait. That answer is different for everyone. I, at the guidance of an anti-divorce author, decided to give it one year after BD. So one year after BD if she wasn't fully recommitted back to the marriage I was going to go file myself. Maybe for you it's 9 months. For some it's 2 years. Some are willing to wait forever. The nice thing about picking a date is that it gives you light at the end of the tunnel, one way or another. No one can blame you for waiting to move on. Also, divorce isn't necessarily the final end that many drum it up to be in their heads. Many couples have divorced and still reconciled.
In the end, it's up to you how long you wait.
M(53), W(54),D(19) M-23, T-25 Bomb Drop - Dec.23, 2017 Ring and Piecing since March 2018