It's always nice to know you are attractive to someone else esp. when you have been rejected by H, but it is not a good idea to get involved in another relationship while still in a mess/quandry/holding pattern with this one. This is the advice my C gave me ages ago and which I found out the hard way is very true. She said you need to be emotionally straight and distant from one before you get into another or it merely becomes a rebound relationship and it doesn't work out. Or you hurt someone else. Or you get hurt again. Although if it was a one night stand of hot sex...hmm...
Anyway, I guess this is why all the advice also says not to snoop (I know you weren't, btw) because you find out things that hurt you and haunt you. Or to never ask a question you aren't prepared to hear the answer to. Perhaps you have reached your limit on being cheery and comforting and upbeat with H. You can only be hurt so many times even from someone you love who isn't doing it to be mean, before you finally say enough and move away. Not necessarily move ON, move AWAY. Perhaps it is time to distance yourself.
I know you are afraid if you do that he will forget or move closer to OW emotionally or decide he doesn't want to come back, etc. but he is going to do what he's going to do regardless. He is already aware of all of it. He knows what you want and where you are. One of your real drawbacks, I think, is H and OW live far apart so it keeps the "excitement" alive for a much longer period than it would otherwise. I'm afraid, PL, that if you really want your H back your only recourse is to wait it out. It could be a long time, too. But I don't see him returning until he has run the course with that tramp. So you need to decide if you want to keep seeing him and dealing with the pain or if you want to distance yourself and deal with the pain. It's a no win situation, unfortunately. But here's the thing while you are deciding. Do what YOU need to do. Not what you think you should do. Or what you think would "work" best. Or what HE might do. But what YOU need and want. The lesser of two evils, so to speak. What will make you feel the least amount of anxiety and pain.
I would NOT call OW. You're right; it will backfire. In the first place, she knows he's married. Do you think she cares how you feel? Forget that. People are very selfish when it comes to affairs of the heart. She will tell H and he will be angry at YOU and will "sympathize" with Ms. Homewrecker and this will push the 2 of you further apart.
And let him tell his parents in his own time. He will appreciate that you did that, sooner or later, when he thinks about it. I agree with you that they should know. But he won't see it that way if you tell them and it will push him further away. Doesn't all this suck big time?!
Of course these are just my opinions and it doesn't mean I am right or you should do everything I say! It just comes from my own experience and seeing it with others. My story is not here because I knew nothing about this board, unfortunately, during my time in hell. I only found this after all was said and done and we were back together.