My boyfriend is texting another girl. Am I overreacting?

This might be long and I apologize but I am really in need out of an outsider’s perspective.

I got into a relationship about three years ago with this guy and it lasted for a year and a half. He was honestly the best guy I’ve ever dated and when I broke it off I was a little scared that I had lost the best thing I would ever find.

I recently moved to the city he relocated to and we got back in touch. We started a relationship because according to him, “he never stopped loving me and over the last year and a half, he was hoping and praying one day he would get another chance”. He tells me this often and actually started crying and pouring his heart out on my couch just about a week ago. However, I had this nagging feeling that this one particular girl that kept calling his phone was a little more than just his friend. Back when we dated, he was always about me and our relationship so for me to think he was entertaining another girl made me feel silly. I told one of my friends and they insisted I was overreacting so I thought I was. One night, I couldn’t help myself and I checked his phone. I always thought I would never be able to say that but over that year and a half, I was made to look like a fool more times than I could count and I didn’t want this to be another one so I was trying to get to it before it got to me. I saw that he was sending her hearts and talking about what a nice day it was to have a picnic date (which is what he actually planned for my birthday). I felt sick to my stomach, I literally left the bed and spent the night in my apartment lobby, thinking. The next day I confronted him, without telling him I went through his phone because I felt terrible about it and I trusted him so much that I wanted to believe he would tell me the truth. I asked if he was seeing someone else and he got really upset, saying that he could never do that to me, he wouldn’t jeopardize our relationship for a girl that he didn’t try for a year and a half to get back, she knew about me and she was a close friend like one of my friends is to me. Mind you, I’ve known him since the first grade and my parents know him – this girl he’s known for a month max and she probably doesn’t even know his mom’s first name. I wanted to believe that he of all people would never hurt me like that so I decided to let it go and move on. We were good for a couple days and then something made me feel like just because I haven’t seen him talk to her doesn’t mean he isn’t. I, then, checked his phone again (and of course hated myself afterward) to find that he was still texting her and sending her hearts and he was most likely calling her when he left my apartment and went to his because he had multiple text messages telling her that he would call later. I haven’t said anything this time and honestly the thought of losing him again kills me. I don’t think I could live with the fact that one, he would do something like this to me and two, that I had to break it off because of him entertaining this girl. On top of the fact, I don’t know how I would because he’d want to know why I did and I just can’t tell him that I went through his phone.

I need advice.

PS: the girl lives about three states away from us and has a boyfriend so I’m not worried about them hooking up, I’m feeling like this is a sign he doesn’t actually care for me the way he used to or is saying that he does. After the last, failed relationships, having someone treat me like crap again would kill me. It has already caused me to have low self-esteem and now this is makes me feel like she’s better than me if he can’t just tell her to back off from the first time I said something.