Should I go?

I've been seeing a guy for the past seven months, and we've faced some challenges in our relationship. One major issue is his close friendship with a girl, for whom he has previously admitted to having feelings. He assured me that nothing physical ever happened between them, but he seems to have held onto those feelings until he met me. As we began dating, I noticed he continued to communicate with her frequently, which made me uncomfortable. I asked him to establish some boundaries, but it doesn't seem like he has enforced them as much as I would prefer. I get the impression that he genuinely cares for her and wants her in his life, which disturbs me, especially given what I know about their history. Recently, he mentioned that they hadn't spoken for about a month and a half, but during the weekend he spent with me, I saw that she messaged him in the morning. That triggered a lot of anxiety for me. It feels like no matter what I do or say, he will always keep her around, and I would need to accept that if I want to be with him. However, I don't think I can accept it after everything we've been through together. Just seeing that one notification has consumed my thoughts for the past two days, and I feel like I need to walk away from this relationship. I could really use some advice on how to handle this situation.