<human>: Can you provide a brief rundown of the text in within 3 sentences?

My boyfriend and I have been together for about a year, and we have had a solid and healthy relationship up to this point. I have never given him any reason to doubt me before, and have been completely faithful to him - I also do not have a history of cheating/lying/deception in my past relationships. I value trust in a committed relationship, and have not acted suspicious or secretive in any way, because I have nothing to hide.

BUT, a few days ago, I picked up my phone and discovered that a conversation with my ex was pulled up, indicating that my boyfriend had been looking through my text messages without my knowledge.  The texts with my ex were innocent and not in any way sexual or emotionally charged. In fact, I had not even responded to several of them because I either forgot or wasn't really that interested in the conversation to begin with. 

When I confronted him, he admitted that he did look through my texts and that he was wrong. When I asked him if he did it because he doesn't trust me, he claimed that he does trust me, but since he's been hurt by his former girlfriends, seeing my ex's number in my phone got the best of him and he looked through my messages out of curiosity. 

I have always heard that if your SO looks through your texts when you aren't around, that they don't trust you and the relationship is probably over. Is this true? Is this no big deal, or does it seem like we might have a bigger problem in our relationship?
<bot>: Always been faithful, but my boyfriend has been reading my texts behind my back. Is there a deeper, underlying trust issue here that needs to be addressed?