How do I get back the old times? Help!?

This is my first relationship and I really dont know what to do.I broke up with my bf last saturday night. I only mailed him that I was breaking up with him (which was totally mean). That time, things were running in my head because he hadn't text or talk to me for two days that's why I decided to end us. My friend talked to me about it because she and I thought that it was what I really want. But then the next day he agreed to end it and he wrote very sad things on fb and even sent me the song "broken strings". while listening to the song, i realized the times we were together. he was such so caring and always expresses his fondness to me. and so i went back with him. he agreed to get back but its not the same (duh). how do I atleast save what we have started? (we're together for 3 weeks until I ruined it)