I've been dancing around with my advice, trying to be objective. I'm going to be a straightshooter and tell you what I would do. Is it the DB thing to do? I don't know. Here's what I would do...
1) I would quit leaving so much to guesswork. You and your W are supposedly getting back together, at least in her words, so I would think that communication shouldn't be a problem. So I would flat out tell her that you saw she had a trip to Spain planned with OM and you want to know what that's about.
Then let her talk. Put her words through a filter and see if it's believable. I don't know about you, but I wouldn't pay for someone's plane ticket if I intended to dump them while on vacation. Personally, my opinion is she's trying to pick which one of you to be with. If it were me, I can tell you that I'd make the decision easier on her by letting her know in no uncertain terms that I wasn't going to be second fiddle.
2) If the affair continued, I'd kick her to the curb and then do whatever I wanted, including moving back to Australia if that's what I felt like doing.
3) I wouldn't get her family involved. It makes reconciliation much harder. Once that cat's out of the bag, there is kind of a reluctance on the part of the WAW to acknowledge that they may be making a mistake. Right now she can return without any egg on her face.
In the end, it's not the years in your life that count. It's the life in your years. Abraham Lincoln
It is hard to fail, but it is worse never to have tried to succeed. Theodore Roosevelt
