dependent on them
can't live without them
think about them all the time
dream about them
wish to be with them
don't want to leave them
afraid they will leave you
want to be by their side all the time
look forward to seeing them
cry as soon as its time to leave
google them and try to find out stuff about their personal lives
if you have a pic, stare at it for hours and imagine you are with them
save their voicemails/emails and listen/read them over and over
cry at night because you want them to hold you

just off the top of my head...