I think my new boyfriend is still in communication with past ex's

My boyfriend and I have been dating for a month now; he's 21, I'm 19. He's amazing and more than I could ever ask for, he's so thoughtful and has never given me a reason to see him as untrustworthy. We had a run in with his most recent ex and we dealt with that together. I read the harrassing texts and what he had to say was "Leave me alone I don't want anything to do with you anymore"- blah blah blah and I was happy with that. But I went through his phone (I know I shouldn't have I just wanted to see) and I noticed a slew of texts from about 2 weeks ago (right around the same time shit was going on with the first ex) from this girl he has mentioned before, not as his ex though but I had speculations. I only had time to skim through a few but it was along the lines of "I'm moving on, your childish, you never texted me back that night.." and just all kinds of confusing shit (that was her text to him). So I want to know although I'm in the wrong for snooping do I ask him if he's in contact with any of his other ex's? And should I be worried that he is? I know we both had other lives before we got in a realtionship, but they are ex's and shouldn't have a part of what him and I have :(