Worried if he likes someone else..?

Im Sixteen years . and hes Fifteen . We have been going out for nearly Five months.

Yesterday my boyfriend came over... and was going through his facebook, he then went on this girls profile.. and hes sister said "He likes her" . I said "I dont think so" . He said nothing.. . She then said "He use to" . But now its got me thinking if he actually still does.. im going to ask him next time i talk to him.. but lieing is soo easy to do!

Anyway.. she lives in a different state.. and for some reason.. i keep imagining her coming back here.. and taking him away from me.. then him leaving me.. and them to falling inlove... :(

Ahh my gosh.. what should i do..