The way I see it is this. The OP doesn't trust his woman and would go off on one over the most innocent of messages or calls found. Then there's the repeated "Are you making the beast with two backs with someone else" questions.
If there's one thing guaranteed to drive her to someone else, it's right there in front of everyone's eyes, and I know what my reaction would be if I found out my missus planted some sort of spyware on my phone (not that she has the tech knowledge to do that without me finding it) whether I was up to something or not.
Bottom line is this. The trust has gone, the relationship is over no matter what because if she is screwing around then he'll never trust her again, and if she isn't then she'll never trust him to believe that any innocent contact with another bloke is something other than innocent contact.
It could well be she's having one last blow out before getting hitched, she wouldn't be the first woman to do so, but the bottom line is what was there will NEVER return no matter how much he "loves" her because he's always going to have this nagging feeling in the back of his mind that there's a third (or more) person in the room, the snooping will go on for the whole duration of what would be a VERY short marriage, the paranoia will only grow.
So there's only one option, one I took myself *ahem* years ago, and end it for the relationship is doomed now no matter what as counselling will only likely unveil some truths that he won't want to hear and make things worse.
It's over, move on