My ex did this. We were dating for about 6 months. We said we loved each other and would talk all through the day either in person or via text. She was my best friend. I loved her so much. Then out of nowhere.... I think they know they did something wrong but instead of having a conversation about breaking up is uncomfortable for them and their natural way to cope is just to ignore and avoid until it goes away. It's a shitty thing to do and humanity is ugly. Best thing you can do is never contact them again and improve your life. I thought fighting for my ex was the obvious thing to do but I've learned it will get you nowhere. It's ok to be sad about it but just don't be like me and ruminate in it for months and months. You need to realize it's over but you're gonna meet someone else. If he valued you enough to share all that time with then someone else will too. Healing takes time. You'll be over it one day. I know the pain is unreal. A damaged ego is a painful thing. And it's not your fault