Don't pay no mind to that I love you line...he either wants attention or want???? so look at him and with a bigger than big grin tell him..."sure you do sweety pie" and tell him to take you shopping to see how long the love will last. :)
In todays world, saying I love you to a girl is only one of many ploys to get her to compromise herself respect, and to get her to do certain things her better judgement would prevent. Any reason we in society see such a sharp rise in teen pregnancy? All too many young males today throw around the word "love " without the needed respect that goes with it. Too many use it to literally "talk the pants off "of their dates! Sad but true. :(
Just say thank you and maybe give him a hug or something. You don't have to say it back just because. This should be an indicator if he is an emotional type, keep that in mind cause his feelings might get hurt easily too. Mind your feelings and where you want this to go, if it is not happening for you back put the brakes on early so hurt is not so bad.