Why does my ex copy me?

My ex and I haven’t talked in a month. He has a girlfriend now. It’s really awkward being around him. I pretend to be over him so I do things to show him and he copies it. Usually when I see him I get on my phone and watch a funny video. I smile at my phone while I’m watching. He thinks that I’m on the phone with a guy. He started doing it too shortly after. I will see him doing nothing but as soon as he sees me, he gets on his phone acting like he’s talking or texting someone. He doesn’t say much when he’s “on the phone” bc I know he’s really not on the phone with anyone.

I’m usually the last person to walk out the class and he knows it. Back then he would wait on me but suddenly stopped I don’t know why.

Now he’s back at it again. He pretends to dig in his bookpack but he’s really waiting on me. Because as soon as I walk past him he follows right behind or side of me. He stares at me expecting me to stare back. I started being the first one to leave class early like I didn’t care for anyone in there and now he’s doing the same. I don’t get him. Why is he copying me?
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I forgot this part. I’m selling these roses as a fundraiser and he brought ALL of them.
Why does my ex copy me?
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