M24 continues to deceive me, F20.

I'm feeling really lost right now, so let me provide some context. My boyfriend and I started dating in July 2023 after meeting on Tinder. Our first date went wonderfully, and by our second date, he asked me to be his girlfriend. I said yes, not realizing I was rushing into things without fully getting to know him. Two months into our relationship, I moved in with him, and we needed to find a new roommate. He announced on Snapchat that we were looking for someone, and a girl responded, claiming to be a “mutual friend from high school.” I took him at his word, and we started discussing her move-in date. However, I started to get an uneasy feeling about the whole situation. One day, he left his Apple Watch behind, and I heard it go off. Out of curiosity, I checked his messages and found her being overly friendly. She even mentioned swinging by his family’s house to grab some things, which confused me because he had told me they didn’t know each other well (can you see where this is heading?). When I confronted him about it, he gave me a weak excuse, and unfortunately, I believed him. As time passed, I had this nagging feeling that something was off, so I looked through his phone and found a message from him asking her why she had texted him on Instagram, to which she replied she was bored. I searched for their communication on Instagram and initially found nothing, but then discovered he had a secret account where he was messaging his ex. I was furious to find out he had been trying to get his ex to move in with us. We argued intensely, and I told him he needed to block her or I would leave. He reluctantly complied but then played this ridiculous game of unblocking her at work and blocking her again when he got home. This has been dragging on for months, and I’m feeling exhausted and unhappy. He's planning to change his number in January, but I’m not sure if I can ever fully trust him again. Today, she called him eight times, and they talked for around three hours. I’m beginning to doubt whether we can work it out, but I don’t know how to express that to him. He keeps saying I can leave if I want to, but it doesn’t feel that simple. My family might let me move back home, but I feel guilty about being a burden since money is tight for them and I wouldn’t even have a room. I want things to work out, but sometimes it feels like I’m talking to a child; he just doesn’t seem to grasp how I feel. If anyone has advice or could offer some validation, I’m really desperate for answers. It feels crazy to think he isn't considering how all of this affects me.