<human>: Can you provide a brief rundown of the text in within 3 sentences?

Me 20/F and my ex 22/M dated for a year (this was a while ago). I came to the realization that we weren't right for each other in that way, but I was panic-y because I didn't want to lose him as a person I valued in my life. So prior to breaking up, he promised me numerous times we would stay friends and that he would always be there for me- this made the break up easier. Since then (closer to the break up time but far away enough to heal) I've tried briefly initiating small conversation to build a friendship. His replies were one worded. At some point I said ok I won't bother him, I'll wait for him to reach out to me. It's been a long time, I want to say half a year and I haven't heard a peep out of him. 

I'm not like super upset over it, I rarely think about it, but when I do- I can't escape the gnawing curiosity as to why he has never ended up reaching out to me. I definitely know it's not because he found another girl (I won't go into detail why I know this). My friends keep saying it's because he was ashamed that he "couldn't give me everything I needed", but that sounds like bullshit. Even shame fades after this fucking long, and all I wanted was to keep this wonderful person in my life. What do you think could've happened?
<bot>: ex-bf promised to be friends forever even after we broke up, haven't heard from him in half a year. why?