It seems to me, if you really want to finish the relationship once and for all, that you should give serious consideration to moving to another city if possible.  Otherwise, as you well said, you will run into him sooner or later since you both share conmon grounds and friends

I've been there, sister. There is only ONE answer. Break off contact. It's gonna hurt, it's gonna be hard. 
But, it's gotta be done. You'll get over it eventually, but it may take a long time. You'll just have to bear it.

Actually, he doesn't mess you up...you do!

Perhaps youi choose to believe him when you know you shouldn't, you say something to not hurt his feelings, you do something which, you just KNOW you really shouldn't... and wham bam, it all comes back again...

Best advice I can offer (other than you so some serious soul-searching to find what it is about him that makes the above happen), is to tell your friends that right now, you just can't deal with anything to do with him.I'm sure they'll understand. Go find some new friends,

Also, what you SERIOUSLY NEED to do is start writing letters. Write a big long letter saying EVERYTHING you've wanted and needed to say to him - all that stuff that you've needed him to understand and completely get. Once you've done that, write his 'reply' to your letter. Write out everthing that he needs to say to you, how you need it to be said, that he gets what you said, and understands it... THEN, write your reply back to 'him', answering h'his' letter to you... and go back and forth like this til IT'S ALL OUT OF YOUR SYSTEM! (no, he, nor anyone else, will ever see those letters.... feel free to burn them after you've done it all!)

"Oh", you say, "what's that gong to achieve?" Well, do it, and find out! I was engaged (briefly) many years ago, and this sort of stuff got me over the break-up pretty quickly! If that's not good enough of an experience for you, then not much other advice is gonig to do any good for you!

 I can't move to onother city coz I am stuent here and thankyou for your suggestion, definately I am going to write it  down, I have tried my way and i failed this time I wana try the way someone already got over this situation.

Take a long hard look at your relationship and think things through when you’re done you should care as much

they say it takes about half the time you were with somebody to get over them.
It took me a few years to get over my ex    but you know what        She did me the biggest favor by kicking me out.
I met the best lady in the world as a result of the break up.
it made me take a good look at myself and what I liked in a person.
Maybe I got lucky but then again maybe it was to be.
you soud young so you will have achance to meet many more intresting people
good and bad.
for now   try changeing your circle of freinds and from there you will have a better chance of meeting diffrent people
good luck and my best regards