I really need opinions

Since October of last year, my partner has been texting a girl occasionally, sometimes all day long. He got caught because when I walked past him he slid off the message and back to YouTube and at first he lied to me, and then I finally got the truth. But everything was deleted when I asked to see the messages but he offered to text or call her to show that he wasn’t hiding anything, and he didn’t want me to txt her. All this happen at the beginning of July 6th this year. They haven’t spoke since that day and she got mad for him telling me her business. I didn’t realize they were texting that much and basically all day long and through early hours of the morning until I went to the call log and went back all the way to the beginning of last year, so a lot was said since then. In my mind is telling me that there was some things inappropriate said, but it’s like I’ll never know the truth. I’m basically left with nothing because everything was deleted. We’ve been together for six years and have three kids together . Part of me wants to text the girl but then again it would just cause a big fight, but I’m still hurt from this day . He also told me he isn’t going to cut her off if one day she messages him he will let me know but will keep talking to her.