how do you cope with someone telling you they love you when you can’t believe it whatsoever

it feels impossible to be true. i know the person isn’t a bad person whatsoever but all it did was leave me with more questions. why do they feel this was. HOW could they feel this way. once they know me more they will not. i feel like shit because i can’t let my guard down. i have an overwhelming amount of guilt. why can’t i just be happy with what i got? why do i have to analyze it ?