Why is he doing this?

In the beginning of the holidays, my ex broke up with me because he didn't feel he same about having a relationship anymore. We were really close friends for quite some time and we made an agreement before he relationship that we would remain close friends.
But when we met up he didn't seem interested in that and also said just friends, so I took that as friends and accepted that. I used the holiday to get over him and I successfully did :)

My ex is in the same friendship group as me and these few days coming back to school have been weird...

When we were close friends we use to talk a lot to each other but obviously we aren't so I talk to other people instead. And whenever he is near me (I mean every time), he talks loudly to people on purpose and goes on about this girl he met and has a liking for. I checked with a couple of my friends who were there just to make sure I wasn't the only person that heard this incase of being paranoid and they agreed with me.

I also noticed that he tried to lean on me one time while he was trying not to make it obvious. So to make sure I again wasn't just making this up in my mind, I would shuffle bit by bit away from him and he would still move close to me and lean on me while talking with other people who were focused on the conversation at the time. The final time I shuffled away, he fully leaned on me so I walked away completely to another place to stand well away from him.

Today I was talking to a boy I'm good friends with and he walked over in front of me on purpose & brushed his bag against me. And he wondered over and coughed sarcastically?
Recently he has been mocking my voice in a joking way (that's basically the only way for him to get me to look at him which I rarely do now). He looks at me when I don't look at him my friends say.

All I ask is your honest opinion from the information I have written down on this situation. Just your own thoughts to why is he acting this way? That would help me so much, thank you!
Why is he doing this?
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