Explaining what happened. Leave advice or opinions

i met my boyfriend around 2022 and we began dating shortly after. we were young at the time-but going pretty well, both in highschool together, both immature and prone to toxic behavior. then around the beginning of 2023ish this guy follows me on instagram, i dm him and hide the chats, it's nothing major just asking about music recs and talking about schoolwork. i talk to him to my girl best friend the way i talked about my current boyfriend, i was slightly interested and curious about him. then my boyfriend finds out and a big fight ensues. i block the guy, never speaking or thinking of him again. we continue our relationship, and i deny being interested in the guy time and time again when it's brought up. Then, yesterday, my boyfriend/ex gets the urge to ask about it, it's clearly been bothering him for some time. He asks me if i was interested in him, rambling on and on about "how it doesn't make sense". i finally admit, "i was vaguely interested in him, but it was just curiosity more than anything". He then, after our whole relationship talk about marriage and even having names picked out for our kids, breaks up with me. We had been smooth sailing for years and we had rebuilt our trust together since then, i don't know why it just happened now instead of then. He said we could work it out but then he just turns around and leaves me. I understand completely that my actions have consequences, and i understand completely what i did was wrong and nothing can justify or explain what i did. We were both stupid teenagers who were toxic and worked out of those ways to become healthy adults having a thriving relationship. Everything was perfect since then, we both didn't watch porn, both looked away when nude scenes popped up on screen, both respected eachother, both had undying love for eachother, and even the night before he took me out to dinner because i was having a bad day at work. He's met my entire family and got along with all of them, came on family trips, was comfortable enough with my family to sleepover. He truly was and is a beautiful soul, and i just wish to come back to him. i just feel so lost, he was my other half, my best friend, and now i don't know what to do. I just cannot grasp how it can be perfect since the incident, the trust is regained, we fix toxic behaviors, then it suddenly gets brought up and he just leaves. I understand my actions are wrong, we ve just worked through so much that this seemed like something we could overcome. but i'm not in his position, i can't say for sure it's possible to regain trust after this. I've talked with him since then and he seemed set that this was the worst thing anyone could do. But talking with my family, his family, and his brother, they are adamant that i didn’t do something as bad as he’s putting it out to be. I clearly was wrong messaging another guy that interested me, and i understand that. Once he found out, something in my brain snapped and i felt like i needed to change from my toxic cycle. I would ve never cheated on my him, but he is stuck in the loop that i would have cheated if he never caught me. I've explained that i messed up, i’ve taken accountability, i've explored different perspectives and tried to understand his. Nonetheless he is adamant that this is the end of our relationship and it’s worse than i can picture it. It's tearing me apart, i've shown him since then that i recognized the wrongdoing in my past relationships and the wrongdoing of being interested and texting another guy. I've shown him that i can change, that i can grow, that i'm able and willing to improve myself for the sake of him and myself.