Undamaged,
Sorry you are here.
Everyone here has had their own experience with a cheater.
1) If he is still angry, he is still lying to you. He should not be defensive, he should be completely open and willing to tell you anything you ask. Otherwise, he will never be able to rebuild trust with you.
2) Even if "nothing happened" physically, something happened. Do not allow him to minimize his betrayal. You'll see a common pattern and advice here. Cheaters deny, minimize, and attempt to rugsweep (get you to ignore what has happened and "just move on" and "make things the way they were before"). You should not allow any of that to happen.
3) If you want to trust him again, come up with a list of demands:
- Show you all the texts, get phone recovery software (Fonelab is often recommended for iPhones).
- No Contact (NC) with the affair partner. You should see what the message says and confirm that it has been sent.
- Written detailed timeline of what happened during the affair.
- Optional, but it helps (I didn't ask, my WW offered, but never scheduled) to get a polygraph. Here you can ask him whatever question you want (did you have sex? is your written timeline accurate?).
- More intelligence gathering. Voice Actuated Recorders (VARs), in the car, at home, wherever he might normally have secret conversations. I personally only kept one on myself to protect myself from false allegations. I've been lucky enough to not have to use it.
You probably won't like becoming a person that has to ask for/do these things, but the alternative is to be in denial, fooling yourself, and continuing to allowed to be hurt.