Is it all in my head?

Me an my boyfriend were just cuddling in bed and i just wondered for the time so when i checked it, the first phone i could reach was his. After i checked the time he had a message on bbm(the joys of social media! /:) an nothing seemed any different but i had a weird urge to play around for a while and this may make me a terrible person and i already feel bad for it but my childish side come out and i decided id change his whatsapp status and by this time id pulled myself back on my bed so my boyfriend saw. But as soon as i clicked on whatsapp there was a chat which didnt look familiar to me and as soon as hed seen i was on there he pulled the phone out of my hand and turned onto his side thinking i wouldnt notice him deleting the chat when i asked him who it was he said "just an old convo from me an you" and when i asked why he deleted it he just respond with "cause" am i taking this out of proportion?