why am I so paranoid?

Minnie • 19/England🌟
I've been seeing this guy for a few weeks now and really like him but for some reason I'm a nervous wreck! I've been very careful not to show this outwardly because I don't want to freak him out as we're both so young (19 and 22). Every time he texts me or snapchats me I think 'he's probably sending this to other girls too I'm just th second option'. I'm so confused as to where this has come from because I've never been cheated on/cheated on anyone and my last relationship of two years was pretty normal. Why can't I trust now??