let me get this straight,
his phone and laptop are off limits to you,
he cheated and he probably continues to talk to her,
he flips the script and tells you that you're insecure,
he thinks you should be able to trust him,
even though his actions show that he can't be trusted?

Is this a pretty good summary?

The next time he's texting,
ask for his phone.

tell him
"Prove to me that I can trust you,
allow me to look at your phone and who you are texting.
If you allow me to look at your phone and go through your messages and if you have nothing to hide from me because there shouldn't be secrets in a marriage, then I will trust you but if you can't do this, then I know I can't trust you and I won't be married to someone who is cheating me and we will need to get a divorce. Don't worry about my insecurities, if you are secure in the fact that what you are doing is NOT wrong, you have nothing to hide from me. If you can't show me your phone and computer, then you do have something to hide."