Did that once when I was 22 years old. Though we've been dating for 2 years, I just didn't felt ready for that at all and neither was I sure if it was him I wanted to be with forever (seemed too much for me). To be honest this surprised me too because he's only 1 year older than me. We stayed for about 4 months and I really thought he was recovering from it. One day he broke up suddenly and went totally NC.
I tried asking for a friendship at least. I requested him twice on facebook; the first time was shortly after the break-up and the second time was recently. No replies. I don't see what's wrong with staying friends with an ex bf. It's been a long while since and I thought he was already over it and we could be friends. Nope.
I don't see what I did wrong. It's like I don't exist to him. I never cheated nor mistreated him. Why treat me this way. I was only trying to make him feel better. I only rejected his proposal but not the whole relationship.