I've read through this thread and a couple things stand out...
As has already been said DOS, you cannot control his thoughts and actions. Someone once told me that it is not the actions of others that cause the sin in your life, it's your reaction.
There are things within your own life that need addressed. Again, as has already been pointed out...Reading someone elses text messages is a violation of trust regardless of the reason.
You also have said that your husband is "keeping things" from you. If this is so, how do you know about the money he gave her, the fact that he "changed his password", the lunches, etc? You sound pretty informed as to what he's up to. Is he really not "keeping" this from you but bragging about it?
There are some very deep issues here, however, the ONLY thing you can do about it is obsess on God more than you obsess on your husband and concentrate on being the women God intends for you to be. Immerse yourself in Him, alone. If YOU stay within HIS perfect will, your destiny will be dictated by God. Your husband may or may not be part of the equation...That is up to God.