I (20F) found chats of my bf (21M) with his childhood girl friend

Me and my bf were watching reels on his phone. When that was happening he was answering to messages on ig. A girls chat was there so I asked who that was. she went on it and I saw multiple back and forth reels being sent on the notes of “when are we going out to drink” type of posts. Scrolling up, I saw multiple convos between them but he was too fast to put it away so all i got the reading was him calling her “mami”. I question him about that and he said in his country it’s normal. Questioning more I found they have been friends since forever and used to date when they were younger. She has always been into him as well, trying to get his attention. He recently went on a boys trip back to his country and saw her. According to him that night it was them and some other friends and they were catching up on the years they hadn’t seen each other and then continued to text afterwards.

What should my next step be? What pisses me off if that he doesn’t let me talk to other guys at all or he would get mad. If this situation was reversed, he would break up with me. If it didn’t look like he was flirting with her, or the fact that he would break up with me if it was me doing this, I would be fine with him meeting with this friend when he went on a trip…but texting afterwards? Idk, i might be in the wrong tho