How should I approach this situation with my ex?

I was with my ex from age 11-17, we're both 18 now. We were each others first love and everything else. The last year of being together we drifted apart because of our busy lives. I found out he was seeing another girl so I confronted him about it and he told me to stay out of his business so I told him to never talk to me again. Well he kept following me around (in and out of school) and staring at me for long periods of time and then he started to "egg on" my friends and show up to their work. Well my friend called him and told him to leave me alone. My exes mom found out what happened and went to the police. My ex then tried to say that I took a baseball bat to his truck, he really wrecked it himself because one of his best friends even showed me texts where he admits to doing it. Well we went to court and the baseball bat charge was dropped obviously but my friend went to jail for "harassing" him when he told him to leave me alone. Me and my ex aren't suppose to talk to each other and we haven't. He's tried to tell one person at school that he has a good idea that I messed up his truck, the kid didn't believe him and instead told me so I went to security and told them about it and how he always stares at me whenever he sees me.

We have the same lunch period and unfortunately all of my friends sit at the other end of his lunch table so I've been sitting there. He stares at me through much of the lunch time and glances over at me a lot. A lot of guys stop by the table and talk to me and one guy who sits at the table likes me a lot as well. Guys also have come up to me and asked for my number while he was sitting right there. Well the last lunch period him and his friend had to sit down at my end of the table because of there not being enough space which pretty much left me and him directly across from each other. I've never looked him or stared at him while sitting at the table. If I look at him its rare and usually from the corner of my eye.

I really want to end this whole fighting because we're both 18 now and we've spent so much time on each other. I'm not saying I want to get back with him just that I think its a waste to lose all of that time on this. My friend told me that me sitting at the table just shows that I don't care about the situation and that I'm above the fighting, is that true? I'm not sure how to do that though? And why does he act like that towards me?
How should I approach this situation with my ex?
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