I agree with this. As much as it hurts you to want to figure out the truth to salvage your parent's marriage, it is not your place to do so. They will drag you through the mud and it WILL take a toll on you.  


I helped my mom uncover many truths about my dad cheating on her, and I was happy to be there to support my mom. However, the whole thing has traumatized me because of what they put me through. Unless you have concrete evidence of your mom cheating, I would recommend you to stay out of it.