Why would he look through my text messages?

Re-posting again. just want more answers........Well me and my ex were in homeroom and i was upset about something that happened at home and he came over and grabbed my hand and started doing this little hand shake thing..idk....and i guess i was looking sad and he asked me what was wrong and i said nothing so he left and went to talk to someone else. He walked by my desk again and asked me what was wrong and i said nothing lol. He walked by third time and grabbed my phone and started looking through it...and i went over and looked over his shoulder and he was looking through my saved messages and i said why are you looking through my saved messages...and he said something idk what....then i went back to my seat and he asked me who is "Limbo" (free stuff i get to my phone) and i just waved him off saying it was nothing...and he said oh i thought it was me then he started laughing....and he looked through my regular messages and then he gave back my phone saying...upgrade lol...(because i need a new phone..and he got a new one over the summer)...why do you think he did that