To me, it sounds at first blush like a WAW conducting an A, even just an EA, possibly. Again, we're not experts, we're just people like you going through crap with our spouses, so please read the resources and really think about it.
If she's MLC, there's very clear guidelines as to how to handle. If she's WAW, there are two paths you can travel and only you can decide.
As for the snooping, only do enough to confirm either way what's going on with her. Don't continue past that, it will only drive you crazy and lower your PMA to a depression level. Plus, don't do anything illegal, GWIM?
