What happened to make my boyfriend break up with me?

you know what I have been in this exact situation… we were together for 3 years before we got engaged .. it was offical with us tho .. we had lived together after the first year of dating but both moved home to save money as I was going back to school .. after 4 months of being engaged he called it all off and left me completly … that was last aug… I have talked to him 4 times since then and then out of the blue about 3 weeks ago he decided he wanted me back .. I have always said he is the only one for me and to this day I still beleive it .. but I didnt take him back … I agreed to meet with him and we just talked (we both have new people in our lives) once he finally left … it hit me … he isnt the one I want anymore .. yes I still love him and care about him but I have some one who is more stable and who is better for me … who knows maybe one day I will end up with him … but as for now I walked away… .. you just have to follow your heart and really sit down and think about what you want with your future .. it may be him now but .. at any moment that could all change .. I beleive if you set them free and they come back a second chance is fine .. but eventually that second chance turns into a third and a forth and becomes a lossing battle … follow your heart .. get your life on track and when that is all said and done .. ask yourself if you really do want him back .. thats what I did and I decided that right now … I didnt want or need him … I still do love him to this very day .. as you will also always love the man in your life .. first love lasts forever!!! sorry its so long and I just blabbed on but I hope it helps a little bit atleast