I would leave things alone and allow God to work on her for a bit.
Hiring a PI is very expensive and even then, you may not find out as much as you would like or what you find out could very well be painful to you. Sometimes it is best to allow nature to take its course and allow the affair to die a slow, natural death and not interfere in the process.
Keep the focus on you. BTW, you are not weak by any means...
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
