Emotional cheating or just friends?

I (f21) found out that my boyfriend (m23) has been talking to a girl (f23) he used to talk to before. So backstory is they used to talk as friends, developed a bond, things got sexual while him and I were together. He cut it off and blocked her, only to not tell me until a couple weeks later. He admitted there was a big part of her, he didn’t like so he couldn’t be with or sleep with her. Last night I saw her name come across his phone while in bed. He cleared it quickly and when I asked about it he blamed it on work notification. He got up to get ready for the gym and when he came back in, I asked again. He was really short and weird about it. He showed me who he recently talked to on Snapchat and said it must’ve been someone’s story. I did some research and found out it was her story. And confronted him in the car after the gym. He said he ran into her while she was working, he added her back, and wanted a friend. They talked a bit on Snapchat but once I found out her unadded her. Nothing sexual. At this point there was no text proof so I couldn’t even see if what he was saying was true. Then he blocked her. I asked why’d he lie and he said he didn’t want me to be mad or upset. Once we got home, he made a couple jabs about me possibly cheating (when I let him go through my phone regularly). Knowing it has been sexual in the past (he says only once) I’m not sure how to feel. Is it emotional cheating or just needing a friend? Should I let him talk to her sometimes or leave her blocked?

TLDR: I found a girl on my boyfriend‘s phone that he used to talk to sexually. He lied when I found a story notification on his phone. I confronted him again and he added her before I could see any of the text. then once I was upset, he blocked her.