Well at first I thought he might be cheating on you but when I got down to the part about the long fights and him taking a stand on the matter I sorta changed my mind. If such a big deal was made about him not letting you see it then I would think he's not cheating because it would be pretty stupid of him to cheat on you and have such a drawn out argument about him withholding the "evidence." The most likely reason he's not letting you see it is because the messages between him and his guy friends include information about your prayer history as that is typically a hot topic (no pun intended) between guys.You said you wouldn't trust him for not letting you see it but he probably feels like you're already not trusting him for demanding to see it. If you value the relationship I'd recommend being the bigger person and dropping it and apologizing. I know that doesn't sound fun but he will really appreciate it and not think you're trying to completely invade his personal life with his friends. If he is cheating on you, you will find out eventually through other means, but demanding to see his text messages is not the way to do it. If you feel like you can't live with yourself knowing evidence for his affair might be in his messages, check his phone when he doesn't know you're doing it. And do not let him catch you. Try to catch his password when he types it in. But the best thing to do in the situation is to stop demanding to see his phone, although from what I've read I doubt you will heed to my advice.