Sigh the stupidity of youth

I'm going into this giant fight with my ex-fiance right now and it really makes me see the plain fact she doesn't understand way to damn much.  Shes 18 I'm 22 surprisingly I've gone through an extreme amount of shit in my life and so has she but the difference is I've learned from my mistakes and I was'nt sheltered.  Through out our relationship things were perfectly fine except for her complete lack of common sense and basic respect aspects.  As time went on I started a night job which really cut down on our time with each other cause while I was awake she was at college and work and when she had free time I was at work or sleeping so the only time we got together was a little here and there and most of the time it was made up of sex.  So that leaves the opening for the blinding emotion of "love" to dim down so you can really begin to see who the person is.  Just in general once that happens in all realationships the decision aspect of it kicks in whether this person really is your other half, are they right for you, and can you see a future with them.  My answer was no we got along on a lot but there were key differences that just did not fit.  I knew that later down the line we would have ended being at each others throats screaming hollering etc.  So in severing our relationship I've tried to explain and answer her questions and give support.  But in doing this it gives her the feeling that I really care and there's a second chance even though I've made it clear that would not happen in 5 or less years until she really experiences and learns from life. I guess the reason why I'm sticking around as support is because during the major break up in my life I never received any closure or support and its all I wanted.  Sigh I hate the fact that even though I'm a giant asshole I have a huge heart.  Now its being obvious that I need to push her away and twist the knife a little more I'll admit I made a major mistake I slept with her after we broke up which is misleading but I've tried to make that peace with that.  Now I have to push her away because even trying to be friends doesn't work we were never friends to begin with so she doesn't know how to be a friend with me.  So tips for all you people out there if you ever break up with someone unless that person knows how to be your friend NEVER fuck them again, do not chat with them, and don't hangout with them.  All your asking for is trouble and some weird clingy stalkerish thing >.<