Relationship issues

The past couple of days my boyfriend and I haven’t been getting along well due to his actions. As I walked past him to close the curtains, I saw that he had switched between a message real fast back to YouTube. I asked him about it, but he didn't tell me the truth. After lying to me, he finally told me he's conversing with an old friend, a 'female'. He didn't want to tell me because I would have asked him a lot of questions about what they're conversing about. Of course I was hurt because this isn’t the first time he has lied to me about the same girl! I asked to see the messages but he deleted them but offer to call her txt her to show me the messages where innocent well she responded and told him she basically doesn’t want to talk to him anymore because he told me her past trauma and now I think he is mad at me because he lost a friend. The first time I was pregnant with our 3rd daughter. I asking him did they exchange numbers or anything and he told me he has known her since 2012 and she randomly texted him after years. Just breaks my heart 3 kids together and 6 years together. I’m so good to him.