I don't think it's a good idea to invade your partners privacy, try asking him and see what he says. If you don't believe him and you can't trust him, maybe you shouldn't be together.
I think my boyfriend's cheating. How can I read his text messages?
He will probably get mad you are invading his privacy and not trust you anymore since he does not do that with you. You should ask him if he is cheating on you and then say something like then if you trust me and want me to trust you let me see your texts. If he says no then he has something to hide. Because my friend her boyfriend lets her read his texts now that is relationship goals.
I don't think it's a good idea! Here is why: Even if he's texting someone else, it might not mean anything; I'm a girl and I'm in a relationship, I love my bf, but I also go on dating websites (I signed up on a few of them l ) and chat with people there. I don't sleep with them, I don't even meet them in real life, I just have fun, flirt and receive compliments. It's no big deal, it doesn't hurt anyone, but it makes me happier and complete
The only real way to read your boyfriend's text messages is to physically read them on his phone. This, of course, would involve you being able to access his phone when he's not around.
Evidence
Another thing to consider is whether your boyfriend would be stupid enough to leave a trail of his infidelity for you to find. It's likely that he'd delete any text messages that would reveal that he'd been cheating on you.
Honesty
The best course of action, in my opinion, is to outright tell your boyfriend that you've been worried about what's going on. He might not like it, especially if he's not actually been cheating on you, but it's better to be honest with him than to sneak around behind his back.
If you're unhappy in your current relationship, you should probably think about whether it's worth sticking around. That being said, you should also consider that you could be wrong, and your boyfriend may be completely committed to you.