> dont ask /b/ for advice etc.
> I asked 4chan but...they suck.

You knew it. But you did it anyway.
That's the same situation here. You knowingly sent your gf to the arms of a male friend for two nights alone in the country of romance. The inevitable happened, and now you're all omg and shit.

I suggest that you guys take some time out, reflect on your innerself, learn tai chi etc.
She probably is fucking him, but to confront her about it would be difficult if you don't want to jeopardise the relationship. Her feminine instincts will deduce that you read her personal messages. And even though she is in the wrong, she'll be the one chucking a physco because you breached her privacy, and therefore disrespected her. Although, it is a worrying point that you're cyberstalking her in the first place.