Well, if you are normally this suspicious, and then ultimately uncaring about your relationship, then chances are you have some problems in your marriage already.
It doesn't sound like you think highly of her at all, or value her much that would be the biggest problem that I can see.
As to the likely hood of her cheating, does she share your lack of interest in your relationship? Even then can't say, I don't know a thing about her.
My advice: Deal with your trust issues and decide if your marriage is actually important to you.