So, basically, my dad is single.  My dad's friend is married.  And I can say with about 95% certainty that I saw them make out next to her car.

I had a feeling this would happen, or already was happening.  He'd been telling me how he felt about her, and I had seen some things that were pretty big tells.  I can't say I disagree, he is a better match for her than the person she's married to, but fuck man I didn't think this shit would actually come to fruition.

I'm not gonna lie, I don't necessarily care that they're cheating.  I'm a neutral party for the most part, but she has two kids.  One is an unstable middle-schooler, and the other isn't even 10 yet.  Additionally, the guy she's with isn't a bad guy.  One thing's for sure, if they get had, the fallout will affect them a lot more than it will me.

I'm not sure what to do, here.  I feel like suddenly I have to try to resolve this situation before things get out of hand.  I know my dad probably won't listen, I've already told him not to do it, so now it seems like I've got two options.  One, I convince her to stop things, which will be difficult because I would hardly ever get a chance to catch her alone, or two, I ignore the situation until shit happens, then do as much damage control as possible.  I'm not going to tell anyone unless asked AND PRESSED about it, because at this point, spilling it is going to do more harm than good.

Anyone have any advice?